/* ===== ROOT & DESIGN TOKENS ===== */
:root {
    /* Colors - Deep Luxury Palette */
    --bg-primary: #07080f;
    --bg-secondary: #0d0f1a;
    --bg-tertiary: #111427;
    --bg-card: rgba(17, 20, 39, 0.7);
    --bg-card-hover: rgba(25, 30, 55, 0.85);
    --bg-glass: rgba(255, 255, 255, 0.03);
    --bg-glass-hover: rgba(255, 255, 255, 0.06);

    --text-primary: #f0f1f7;
    --text-secondary: #9da3bf;
    --text-tertiary: #6b7196;
    --text-muted: #4a4f72;

    /* Gradient Accent */
    --accent-start: #6366f1;
    --accent-mid: #8b5cf6;
    --accent-end: #06b6d4;
    --gradient-primary: linear-gradient(135deg, var(--accent-start), var(--accent-end));
    --gradient-glow: linear-gradient(135deg, rgba(99, 102, 241, 0.15), rgba(6, 182, 212, 0.15));
    --gradient-text: linear-gradient(135deg, #818cf8, #06b6d4);

    /* Borders */
    --border-subtle: rgba(255, 255, 255, 0.06);
    --border-light: rgba(255, 255, 255, 0.1);
    --border-accent: rgba(99, 102, 241, 0.3);

    /* Shadows */
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 8px 32px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 16px 64px rgba(0, 0, 0, 0.5);
    --shadow-glow: 0 0 60px rgba(99, 102, 241, 0.1);

    /* Font */
    --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-display: 'Space Grotesk', 'Inter', sans-serif;

    /* Spacing */
    --section-padding: 120px 0;
    --container-max: 1280px;
    --container-padding: 0 32px;

    /* Radius */
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 24px;

    /* Transitions */
    --transition-fast: 0.15s ease;
    --transition-base: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-smooth: 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ===== RESET & BASE ===== */
*, *::before, *::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    scroll-padding-top: 80px;
}

body {
    font-family: var(--font-primary);
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    overflow-x: hidden;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

a {
    text-decoration: none;
    color: inherit;
    transition: var(--transition-base);
}

button {
    border: none;
    background: none;
    cursor: pointer;
    font-family: inherit;
    color: inherit;
}

input[type="number"] {
    -moz-appearance: textfield;
}

input[type="number"]::-webkit-outer-spin-button,
input[type="number"]::-webkit-inner-spin-button {
    -webkit-appearance: none;
}

/* ===== AMBIENT BACKGROUND ===== */
.ambient-bg {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 0;
    overflow: hidden;
}

.orb {
    position: absolute;
    border-radius: 50%;
    filter: blur(120px);
    opacity: 0.4;
}

.orb-1 {
    width: 600px;
    height: 600px;
    background: radial-gradient(circle, rgba(99, 102, 241, 0.15), transparent 70%);
    top: -200px;
    right: -100px;
    animation: orbFloat1 20s ease-in-out infinite;
}

.orb-2 {
    width: 500px;
    height: 500px;
    background: radial-gradient(circle, rgba(6, 182, 212, 0.12), transparent 70%);
    bottom: -150px;
    left: -150px;
    animation: orbFloat2 25s ease-in-out infinite;
}

.orb-3 {
    width: 400px;
    height: 400px;
    background: radial-gradient(circle, rgba(139, 92, 246, 0.1), transparent 70%);
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    animation: orbFloat3 30s ease-in-out infinite;
}

.grid-overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-image:
        linear-gradient(rgba(255, 255, 255, 0.015) 1px, transparent 1px),
        linear-gradient(90deg, rgba(255, 255, 255, 0.015) 1px, transparent 1px);
    background-size: 60px 60px;
}

@keyframes orbFloat1 {
    0%, 100% { transform: translate(0, 0) scale(1); }
    33% { transform: translate(-80px, 60px) scale(1.1); }
    66% { transform: translate(40px, -30px) scale(0.9); }
}

@keyframes orbFloat2 {
    0%, 100% { transform: translate(0, 0) scale(1); }
    33% { transform: translate(60px, -40px) scale(1.15); }
    66% { transform: translate(-50px, 30px) scale(0.85); }
}

@keyframes orbFloat3 {
    0%, 100% { transform: translate(-50%, -50%) scale(1); }
    50% { transform: translate(-50%, -50%) scale(1.3); }
}

/* ===== NAVBAR ===== */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 1000;
    padding: 16px 0;
    transition: var(--transition-smooth);
    background: transparent;
}

.navbar.scrolled {
    background: rgba(7, 8, 15, 0.85);
    backdrop-filter: blur(20px) saturate(1.5);
    -webkit-backdrop-filter: blur(20px) saturate(1.5);
    border-bottom: 1px solid var(--border-subtle);
    padding: 10px 0;
}

.nav-container {
    max-width: var(--container-max);
    margin: 0 auto;
    padding: var(--container-padding);
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.nav-logo {
    display: flex;
    align-items: center;
    gap: 10px;
    flex-shrink: 0;
}

.logo-icon {
    width: 40px;
    height: 40px;
}

.logo-text {
    font-family: var(--font-display);
    font-size: 1.35rem;
    font-weight: 700;
    letter-spacing: -0.02em;
}

.logo-accent {
    background: var(--gradient-text);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.nav-links {
    display: flex;
    align-items: center;
    gap: 8px;
}

.nav-link {
    padding: 8px 16px;
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--text-secondary);
    border-radius: var(--radius-sm);
    transition: var(--transition-base);
}

.nav-link:hover {
    color: var(--text-primary);
    background: var(--bg-glass-hover);
}

.nav-cta {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 10px 20px;
    font-size: 0.875rem;
    font-weight: 600;
    color: #fff;
    background: var(--gradient-primary);
    border-radius: var(--radius-md);
    transition: var(--transition-base);
    box-shadow: 0 4px 15px rgba(99, 102, 241, 0.3);
}

.nav-cta:hover {
    transform: translateY(-1px);
    box-shadow: 0 6px 25px rgba(99, 102, 241, 0.4);
}

.mobile-menu-btn {
    display: none;
    flex-direction: column;
    gap: 5px;
    padding: 6px;
}

.mobile-menu-btn span {
    width: 22px;
    height: 2px;
    background: var(--text-primary);
    border-radius: 2px;
    transition: var(--transition-base);
}

/* ===== HERO ===== */
.hero {
    position: relative;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    padding: 120px 0 60px;
    z-index: 1;
}

.hero-container {
    max-width: var(--container-max);
    margin: 0 auto;
    padding: var(--container-padding);
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 60px;
    align-items: center;
}

.hero-badge {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 6px 16px;
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--accent-start);
    background: rgba(99, 102, 241, 0.08);
    border: 1px solid rgba(99, 102, 241, 0.15);
    border-radius: 50px;
    margin-bottom: 24px;
    text-transform: uppercase;
    letter-spacing: 0.08em;
}

.badge-dot {
    width: 6px;
    height: 6px;
    background: var(--accent-start);
    border-radius: 50%;
    animation: pulse 2s ease-in-out infinite;
}

@keyframes pulse {
    0%, 100% { opacity: 1; transform: scale(1); }
    50% { opacity: 0.5; transform: scale(1.5); }
}

.hero-title {
    font-family: var(--font-display);
    font-size: clamp(2.5rem, 5vw, 4.5rem);
    font-weight: 800;
    line-height: 1.1;
    letter-spacing: -0.03em;
    margin-bottom: 24px;
}

.gradient-text {
    background: var(--gradient-text);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-description {
    font-size: 1.1rem;
    color: var(--text-secondary);
    line-height: 1.7;
    max-width: 520px;
    margin-bottom: 36px;
}

.hero-actions {
    display: flex;
    gap: 16px;
    margin-bottom: 48px;
}

.btn {
    display: inline-flex;
    align-items: center;
    gap: 10px;
    padding: 14px 28px;
    font-size: 0.95rem;
    font-weight: 600;
    border-radius: var(--radius-md);
    transition: var(--transition-base);
}

.btn-primary {
    color: #fff;
    background: var(--gradient-primary);
    box-shadow: 0 4px 20px rgba(99, 102, 241, 0.35);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 30px rgba(99, 102, 241, 0.5);
}

.btn-secondary {
    color: var(--text-secondary);
    border: 1px solid var(--border-light);
    background: var(--bg-glass);
}

.btn-secondary:hover {
    color: var(--text-primary);
    border-color: var(--border-accent);
    background: var(--bg-glass-hover);
}

.hero-stats {
    display: flex;
    align-items: center;
    gap: 28px;
}

.hero-stat {
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.stat-number {
    font-family: var(--font-display);
    font-size: 2rem;
    font-weight: 700;
    background: var(--gradient-text);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.stat-label {
    font-size: 0.8rem;
    color: var(--text-tertiary);
    text-transform: uppercase;
    letter-spacing: 0.1em;
}

.hero-stat-divider {
    width: 1px;
    height: 40px;
    background: var(--border-subtle);
}

/* Hero Visual - Tank Canvas */
.hero-visual {
    display: flex;
    justify-content: center;
    align-items: center;
    position: relative;
}

.hero-tank-container {
    position: relative;
    width: 500px;
    height: 500px;
}

#heroTankCanvas {
    width: 100%;
    height: 100%;
}

.tank-glow {
    position: absolute;
    bottom: 20%;
    left: 50%;
    transform: translateX(-50%);
    width: 250px;
    height: 100px;
    background: radial-gradient(ellipse, rgba(99, 102, 241, 0.2), transparent 70%);
    filter: blur(30px);
    pointer-events: none;
}

.hero-scroll-indicator {
    position: absolute;
    bottom: 30px;
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 8px;
    color: var(--text-muted);
    font-size: 0.75rem;
    letter-spacing: 0.1em;
    text-transform: uppercase;
}

.scroll-arrow {
    animation: scrollBounce 2s ease-in-out infinite;
}

@keyframes scrollBounce {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(6px); }
}

/* ===== SECTIONS SHARED ===== */
.section-container {
    max-width: var(--container-max);
    margin: 0 auto;
    padding: var(--container-padding);
}

.section-header {
    text-align: center;
    margin-bottom: 64px;
}

.section-tag {
    display: inline-block;
    padding: 6px 16px;
    font-size: 0.75rem;
    font-weight: 700;
    color: var(--accent-start);
    background: rgba(99, 102, 241, 0.08);
    border: 1px solid rgba(99, 102, 241, 0.12);
    border-radius: 50px;
    text-transform: uppercase;
    letter-spacing: 0.12em;
    margin-bottom: 20px;
}

.section-title {
    font-family: var(--font-display);
    font-size: clamp(1.8rem, 3.5vw, 3rem);
    font-weight: 800;
    letter-spacing: -0.02em;
    margin-bottom: 16px;
}

.section-subtitle {
    font-size: 1.05rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto;
    line-height: 1.7;
}

/* ===== HOW IT WORKS ===== */
.how-it-works {
    padding: var(--section-padding);
    position: relative;
    z-index: 1;
}

.steps-grid {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 20px;
}

.step-card {
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-xl);
    padding: 40px 32px;
    text-align: center;
    max-width: 300px;
    position: relative;
    transition: var(--transition-base);
}

.step-card::before {
    content: attr(data-step);
    position: absolute;
    top: -14px;
    left: 50%;
    transform: translateX(-50%);
    font-family: var(--font-display);
    font-size: 0.7rem;
    font-weight: 700;
    color: #fff;
    background: var(--gradient-primary);
    padding: 4px 14px;
    border-radius: 50px;
    letter-spacing: 0.1em;
}

.step-card:hover {
    background: var(--bg-card-hover);
    border-color: var(--border-accent);
    transform: translateY(-4px);
    box-shadow: var(--shadow-glow);
}

.step-icon {
    width: 64px;
    height: 64px;
    margin: 0 auto 20px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(99, 102, 241, 0.08);
    border-radius: var(--radius-lg);
    color: var(--accent-start);
}

.step-icon svg {
    width: 32px;
    height: 32px;
}

.step-title {
    font-family: var(--font-display);
    font-size: 1.15rem;
    font-weight: 700;
    margin-bottom: 12px;
}

.step-desc {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

.step-connector {
    width: 80px;
    flex-shrink: 0;
    opacity: 0.5;
}

.step-connector svg {
    width: 100%;
}

/* ===== CALCULATOR SECTION ===== */
.calculator-section {
    padding: var(--section-padding);
    position: relative;
    z-index: 1;
    background: linear-gradient(180deg, transparent, rgba(99, 102, 241, 0.02) 30%, rgba(6, 182, 212, 0.02) 70%, transparent);
}

.calculator-layout {
    display: grid;
    grid-template-columns: 320px 1fr 320px;
    gap: 24px;
    align-items: start;
}

.calc-card {
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-xl);
    padding: 24px;
    backdrop-filter: blur(10px);
    transition: var(--transition-base);
}

.calc-card:hover {
    border-color: rgba(255, 255, 255, 0.08);
}

.calc-card + .calc-card {
    margin-top: 16px;
}

.calc-card-title {
    display: flex;
    align-items: center;
    gap: 10px;
    font-family: var(--font-display);
    font-size: 0.95rem;
    font-weight: 700;
    margin-bottom: 20px;
    color: var(--text-primary);
}

.calc-card-title svg {
    color: var(--accent-start);
    flex-shrink: 0;
}

/* Tank Type Dropdown */
.tank-type-dropdown {
    position: relative;
    margin-bottom: 16px;
}

.tank-select {
    width: 100%;
    padding: 12px 42px 12px 16px;
    font-family: var(--font-primary);
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-primary);
    background: rgba(255, 255, 255, 0.04);
    border: 1px solid var(--border-light);
    border-radius: var(--radius-md);
    outline: none;
    cursor: pointer;
    appearance: none;
    -webkit-appearance: none;
    transition: var(--transition-base);
}

.tank-select:focus {
    border-color: var(--accent-start);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.12);
}

.tank-select optgroup {
    font-weight: 700;
    color: #818cf8;
    background: #111427;
    font-size: 0.85rem;
}

.tank-select option {
    font-weight: 500;
    color: var(--text-primary);
    background: #111427;
    padding: 8px;
}

.select-arrow {
    position: absolute;
    right: 14px;
    top: 50%;
    transform: translateY(-50%);
    color: var(--text-muted);
    pointer-events: none;
}

.tank-type-pills {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
}

.type-pill {
    padding: 5px 12px;
    font-size: 0.72rem;
    font-weight: 600;
    color: var(--text-tertiary);
    background: rgba(255, 255, 255, 0.03);
    border: 1px solid var(--border-subtle);
    border-radius: 50px;
    cursor: pointer;
    transition: var(--transition-base);
    white-space: nowrap;
}

.type-pill:hover {
    color: var(--text-primary);
    border-color: var(--border-light);
    background: rgba(255, 255, 255, 0.06);
}

.type-pill.active {
    color: #fff;
    background: rgba(99, 102, 241, 0.2);
    border-color: var(--accent-start);
}

/* Dimension Inputs */
.inputs-grid {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.input-group {
    display: flex;
    flex-direction: column;
    gap: 6px;
}

.input-label {
    font-size: 0.78rem;
    font-weight: 600;
    color: var(--text-tertiary);
    text-transform: uppercase;
    letter-spacing: 0.08em;
}

.input-field {
    display: flex;
    align-items: center;
    background: rgba(255, 255, 255, 0.03);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-sm);
    overflow: hidden;
    transition: var(--transition-base);
}

.input-field:focus-within {
    border-color: var(--accent-start);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

.input-field input {
    flex: 1;
    padding: 10px 14px;
    background: transparent;
    border: none;
    outline: none;
    font-family: var(--font-primary);
    font-size: 0.95rem;
    font-weight: 500;
    color: var(--text-primary);
    min-width: 0;
}

.input-field input::placeholder {
    color: var(--text-muted);
}

.input-suffix {
    padding: 10px 14px;
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-muted);
    background: rgba(255, 255, 255, 0.02);
    border-left: 1px solid var(--border-subtle);
    min-width: 45px;
    text-align: center;
}

/* Per-field unit select dropdown */
.input-unit-select {
    padding: 10px 8px;
    font-family: var(--font-primary);
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--accent-start);
    background: rgba(99, 102, 241, 0.06);
    border: none;
    border-left: 1px solid var(--border-subtle);
    outline: none;
    cursor: pointer;
    appearance: none;
    -webkit-appearance: none;
    min-width: 52px;
    text-align: center;
    transition: var(--transition-base);
}

.input-unit-select:focus {
    background: rgba(99, 102, 241, 0.12);
}

.input-unit-select option {
    background: #111427;
    color: var(--text-primary);
}


/* ===== TANK DIAGRAM ===== */
.calc-visual {
    display: flex;
    justify-content: center;
    align-items: flex-start;
    position: sticky;
    top: 100px;
}

.tank-diagram-wrapper {
    position: relative;
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-xl);
    padding: 24px;
    width: 100%;
    max-width: 540px;
}

.diagram-label {
    text-align: center;
    font-size: 0.75rem;
    font-weight: 700;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.12em;
    margin-bottom: 12px;
}

#tankDiagram {
    width: 100%;
    height: auto;
    display: block;
}

.diagram-controls {
    display: flex;
    gap: 8px;
    position: absolute;
    bottom: 36px;
    right: 36px;
}

.diagram-ctrl-btn {
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(255, 255, 255, 0.05);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-sm);
    color: var(--text-tertiary);
    transition: var(--transition-base);
}

.diagram-ctrl-btn:hover {
    background: rgba(99, 102, 241, 0.1);
    border-color: var(--border-accent);
    color: var(--accent-start);
}

/* ===== RESULTS ===== */
.results-card .result-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 12px 0;
}

.results-card .result-item + .result-item {
    border-top: 1px solid var(--border-subtle);
}

.result-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    font-weight: 500;
}

.result-value-wrap {
    display: flex;
    align-items: baseline;
    gap: 6px;
}

.result-value {
    font-family: var(--font-display);
    font-size: 1.05rem;
    font-weight: 700;
    color: var(--text-primary);
}

.result-unit {
    font-size: 0.75rem;
    color: var(--text-muted);
    font-weight: 600;
}

.primary-result {
    padding: 16px 0 !important;
}

.primary-result .result-value {
    font-size: 1.5rem;
    background: var(--gradient-text);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.primary-result .result-unit {
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.result-divider {
    height: 1px;
    background: var(--gradient-primary);
    opacity: 0.2;
    margin: 4px 0;
}

/* Conversion Card */
.conversion-card {
    margin-top: 16px;
}

.conversion-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 10px;
}

.conv-item {
    display: flex;
    flex-direction: column;
    gap: 2px;
    padding: 10px 12px;
    background: rgba(255, 255, 255, 0.02);
    border-radius: var(--radius-sm);
    border: 1px solid var(--border-subtle);
}

.conv-val {
    font-family: var(--font-display);
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-primary);
}

.conv-label {
    font-size: 0.7rem;
    color: var(--text-muted);
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* ===== FEATURES ===== */
.features {
    padding: var(--section-padding);
    position: relative;
    z-index: 1;
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
}

.feature-card {
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-xl);
    padding: 36px 28px;
    transition: var(--transition-base);
    position: relative;
    overflow: hidden;
}

.feature-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 2px;
    background: var(--gradient-primary);
    opacity: 0;
    transition: var(--transition-base);
}

.feature-card:hover {
    background: var(--bg-card-hover);
    border-color: var(--border-accent);
    transform: translateY(-4px);
    box-shadow: var(--shadow-glow);
}

.feature-card:hover::before {
    opacity: 1;
}

.feature-icon {
    width: 56px;
    height: 56px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(99, 102, 241, 0.08);
    border-radius: var(--radius-lg);
    margin-bottom: 20px;
    color: var(--accent-start);
    transition: var(--transition-base);
}

.feature-card:hover .feature-icon {
    background: rgba(99, 102, 241, 0.15);
}

.feature-icon svg {
    width: 28px;
    height: 28px;
}

.feature-card h3,
.feature-card .feature-title {
    font-family: var(--font-display);
    font-size: 1.1rem;
    font-weight: 700;
    margin-bottom: 10px;
    color: var(--text-primary);
}

.feature-card p:not(.feature-title) {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* ===== HOW CALCULATOR WORKS ===== */
.how-calc-works-section {
    padding: var(--section-padding);
    position: relative;
    z-index: 1;
}

.how-calc-content {
    max-width: 1120px;
    margin: 0 auto;
}

.how-calc-prose {
    max-width: 880px;
    margin: 0 auto 40px;
    text-align: left;
}

.how-calc-prose p {
    font-size: 0.95rem;
    color: var(--text-secondary);
    line-height: 1.8;
    margin-bottom: 12px;
}

.how-calc-prose p strong {
    color: var(--text-primary);
    font-weight: 600;
}

.how-calc-prose > p:first-child {
    margin-bottom: 18px;
    color: var(--text-primary);
    font-size: 1.05rem;
    line-height: 1.75;
}

.how-calc-prose > p:last-child {
    margin-top: 20px;
    margin-bottom: 0;
    color: var(--text-tertiary);
    font-weight: 600;
}

.how-calc-bottom-note {
    margin-top: 40px;
    margin-bottom: 0;
    padding: 24px 32px;
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-lg);
}

.how-calc-bottom-note p {
    text-align: left;
    margin-bottom: 0;
    font-size: 0.88rem;
}

.how-calc-grid {
    display: grid;
    grid-template-columns: repeat(5, minmax(0, 1fr));
    gap: 16px;
}

.how-calc-card {
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-lg);
    padding: 24px 20px;
    text-align: center;
    transition: var(--transition-base);
    opacity: 0;
    transform: translateY(30px);
}

.how-calc-card.animate-in {
    opacity: 1;
    transform: translateY(0);
}

.how-calc-card:hover {
    border-color: var(--border-accent);
    transform: translateY(-4px);
    box-shadow: var(--shadow-glow);
}

.how-calc-card-icon {
    width: 44px;
    height: 44px;
    margin: 0 auto 14px;
    color: #818cf8;
}

.how-calc-card-icon svg {
    width: 100%;
    height: 100%;
}

.how-calc-card-title {
    font-family: var(--font-display);
    font-size: 0.9rem;
    font-weight: 700;
    margin-bottom: 10px;
    color: var(--text-primary);
}

.how-calc-card-desc {
    font-size: 0.82rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* ===== FORMULA REFERENCE ===== */
.formula-reference-section {
    padding: var(--section-padding);
    position: relative;
    z-index: 1;
    background: linear-gradient(180deg, transparent, rgba(6, 182, 212, 0.01) 50%, transparent);
}

.formula-ref-intro {
    max-width: 800px;
    margin: 0 auto 48px;
    text-align: center;
}

.formula-ref-intro p {
    font-size: 0.95rem;
    color: var(--text-secondary);
    line-height: 1.7;
}

.formula-ref-intro p strong {
    color: var(--text-primary);
}

.formula-ref-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
    margin-bottom: 32px;
}

.formula-ref-card {
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-xl);
    padding: 28px 24px;
    transition: var(--transition-base);
    opacity: 0;
    transform: translateY(30px);
}

.formula-ref-card.animate-in {
    opacity: 1;
    transform: translateY(0);
}

.formula-ref-card:hover {
    border-color: var(--border-accent);
    box-shadow: var(--shadow-glow);
}

.formula-ref-header {
    display: flex;
    align-items: center;
    gap: 14px;
    margin-bottom: 18px;
}

.formula-ref-icon {
    width: 48px;
    height: 48px;
    flex-shrink: 0;
}

.formula-ref-icon svg {
    width: 100%;
    height: 100%;
}

.formula-ref-shape {
    font-family: var(--font-display);
    font-size: 0.95rem;
    font-weight: 700;
    color: var(--text-primary);
}

.formula-ref-expression {
    background: rgba(99, 102, 241, 0.06);
    border-radius: var(--radius-sm);
    padding: 14px 18px;
    margin-bottom: 16px;
    color: #818cf8;
    font-family: 'Space Grotesk', monospace;
    font-size: 1.1rem;
    font-weight: 700;
    text-align: center;
}

.formula-ref-variables {
    display: flex;
    flex-direction: column;
    gap: 4px;
    margin-bottom: 20px;
    padding: 0 4px;
}

.formula-ref-variables span {
    font-size: 0.82rem;
    color: var(--text-secondary);
}

.formula-ref-variables strong {
    color: #818cf8;
    font-weight: 700;
}

.formula-ref-example {
    background: rgba(255, 255, 255, 0.02);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-md);
    padding: 18px;
}

.formula-ref-example-title {
    font-family: var(--font-display);
    font-size: 0.78rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--accent-end);
    margin-bottom: 10px;
}

.formula-ref-example p {
    font-size: 0.82rem;
    color: var(--text-secondary);
    line-height: 1.6;
    margin-bottom: 10px;
}

.formula-ref-calc {
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.formula-ref-calc span {
    font-family: 'Space Grotesk', monospace;
    font-size: 0.82rem;
    color: var(--text-secondary);
}

.formula-ref-calc strong {
    color: var(--text-primary);
}

.formula-ref-note {
    margin-top: 10px;
    font-size: 0.78rem !important;
    color: var(--text-tertiary) !important;
    font-style: italic;
}

.formula-ref-conversion-note {
    max-width: 800px;
    margin: 0 auto;
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-lg);
    padding: 24px 32px;
}

.formula-ref-conversion-title {
    font-family: var(--font-display);
    font-size: 0.85rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 8px;
}

.formula-ref-conversion-note p:last-child {
    font-size: 0.88rem;
    color: var(--text-secondary);
    line-height: 1.7;
}

/* ===== COMPARISON CHART ===== */
.comparison-chart-section {
    padding: var(--section-padding);
    position: relative;
    z-index: 1;
}

.comparison-intro {
    max-width: 800px;
    margin: 0 auto 40px;
    text-align: center;
}

.comparison-intro p {
    font-size: 0.95rem;
    color: var(--text-secondary);
    line-height: 1.7;
}

.comparison-intro p strong {
    color: var(--text-primary);
}

.comparison-table-wrapper {
    max-width: 1100px;
    margin: 0 auto 40px;
    overflow-x: auto;
    border-radius: var(--radius-xl);
    border: 1px solid var(--border-subtle);
    background: var(--bg-card);
    scrollbar-width: thin;
    scrollbar-color: rgba(99, 102, 241, 0.3) transparent;
}

.comparison-table-wrapper::-webkit-scrollbar {
    height: 6px;
}

.comparison-table-wrapper::-webkit-scrollbar-track {
    background: transparent;
}

.comparison-table-wrapper::-webkit-scrollbar-thumb {
    background: rgba(99, 102, 241, 0.3);
    border-radius: 3px;
}

.comparison-table {
    width: 100%;
    border-collapse: collapse;
    min-width: 700px;
}

.comparison-table thead {
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.12), rgba(6, 182, 212, 0.12));
}

.comparison-table th {
    font-family: var(--font-display);
    font-size: 0.8rem;
    font-weight: 700;
    color: var(--text-primary);
    text-transform: uppercase;
    letter-spacing: 0.06em;
    padding: 16px 18px;
    text-align: left;
    white-space: nowrap;
    border-bottom: 1px solid var(--border-light);
}

.comparison-table td {
    font-size: 0.85rem;
    color: var(--text-secondary);
    padding: 13px 18px;
    border-bottom: 1px solid var(--border-subtle);
    line-height: 1.5;
}

.comparison-table tbody tr:last-child td {
    border-bottom: none;
}

.comparison-table tbody tr:hover {
    background: rgba(99, 102, 241, 0.04);
}

.comparison-table tbody tr:hover td {
    color: var(--text-primary);
}

.comparison-table td:first-child {
    font-weight: 600;
    color: var(--text-primary);
    white-space: nowrap;
}

.comparison-table td:nth-child(3),
.comparison-table td:nth-child(4) {
    font-family: 'Space Grotesk', monospace;
    font-weight: 600;
    white-space: nowrap;
}

.comparison-notes {
    max-width: 1100px;
    margin: 0 auto;
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 20px;
}

.comparison-note-item {
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-lg);
    padding: 24px;
    transition: var(--transition-base);
}

.comparison-note-item:hover {
    border-color: var(--border-accent);
}

.comparison-note-title {
    font-family: var(--font-display);
    font-size: 0.88rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 10px;
}

.comparison-note-item p:last-child {
    font-size: 0.85rem;
    color: var(--text-secondary);
    line-height: 1.7;
}

/* ===== FORMULAS ===== */
.formulas-section {
    padding: var(--section-padding);
    position: relative;
    z-index: 1;
    background: linear-gradient(180deg, transparent, rgba(99, 102, 241, 0.015) 50%, transparent);
}

.formulas-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 20px;
}

.formula-card {
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-xl);
    padding: 32px 24px;
    text-align: center;
    transition: var(--transition-base);
}

.formula-card:hover {
    border-color: var(--border-accent);
    transform: translateY(-4px);
    box-shadow: var(--shadow-glow);
}

.formula-shape-icon {
    width: 80px;
    height: 80px;
    margin: 0 auto 20px;
}

.formula-shape-icon svg {
    width: 100%;
    height: 100%;
}

.formula-card h3,
.formula-card .formula-title {
    font-family: var(--font-display);
    font-size: 1rem;
    font-weight: 700;
    margin-bottom: 16px;
    color: var(--text-primary);
}

.formula-display {
    font-family: 'Space Grotesk', monospace;
    font-size: 1.2rem;
    font-weight: 700;
    background: var(--gradient-text);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    padding: 12px 16px;
    background-color: rgba(99, 102, 241, 0.06);
    border-radius: var(--radius-sm);
    margin-bottom: 16px;
    /* Need to use a different approach for text gradient with background */
    position: relative;
}

.formula-display {
    background: rgba(99, 102, 241, 0.06);
    border-radius: var(--radius-sm);
    padding: 12px 16px;
    margin-bottom: 16px;
    color: #818cf8;
    font-family: 'Space Grotesk', monospace;
    font-size: 1.15rem;
    font-weight: 700;
}

.formula-card p {
    font-size: 0.85rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* ===== CALCULATOR ANATOMY GUIDE ===== */
.calculator-anatomy {
    margin-top: 72px;
    scroll-margin-top: 100px;
}

.anatomy-wrapper {
    max-width: 800px;
    margin: 0 auto;
}

.anatomy-selector {
    display: flex;
    justify-content: center;
    gap: 8px;
    margin-bottom: 32px;
}

.anatomy-btn {
    padding: 10px 24px;
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--text-secondary);
    background: var(--bg-glass);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-sm);
    transition: var(--transition-base);
    overflow-wrap: anywhere;
}

.anatomy-btn:hover {
    border-color: var(--border-light);
    color: var(--text-primary);
}

.anatomy-btn.active {
    background: rgba(99, 102, 241, 0.1);
    border-color: var(--accent-start);
    color: var(--text-primary);
}

.anatomy-canvas-wrap {
    position: relative;
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-xl);
    padding: 32px;
    overflow: hidden;
}

#anatomyCanvas {
    width: 100%;
    height: auto;
    display: block;
}

.anatomy-tooltip {
    position: absolute;
    padding: 10px 16px;
    background: rgba(7, 8, 15, 0.95);
    border: 1px solid var(--border-accent);
    border-radius: var(--radius-sm);
    font-size: 0.82rem;
    color: var(--text-primary);
    pointer-events: none;
    opacity: 0;
    transform: translateY(4px);
    transition: opacity 0.2s, transform 0.2s;
    z-index: 10;
    max-width: 200px;
    line-height: 1.5;
    box-shadow: var(--shadow-md);
}

.anatomy-tooltip.visible {
    opacity: 1;
    transform: translateY(0);
}

/* ===== FAQ ===== */
.faq-section {
    padding: var(--section-padding);
    position: relative;
    z-index: 1;
}

.faq-grid {
    max-width: 760px;
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.faq-item {
    background: var(--bg-card);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-lg);
    overflow: hidden;
    transition: var(--transition-base);
}

.faq-item:hover {
    border-color: rgba(255, 255, 255, 0.08);
}

.faq-item.open {
    border-color: var(--border-accent);
}

.faq-question {
    width: 100%;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px 24px;
    font-size: 0.95rem;
    font-weight: 600;
    text-align: left;
    color: var(--text-primary);
    transition: var(--transition-base);
}

.faq-question:hover {
    color: #818cf8;
}

.faq-chevron {
    flex-shrink: 0;
    transition: transform 0.3s ease;
    color: var(--text-muted);
}

.faq-item.open .faq-chevron {
    transform: rotate(180deg);
    color: var(--accent-start);
}

.faq-answer {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.faq-item.open .faq-answer {
    max-height: 300px;
}

.faq-answer p {
    padding: 0 24px 20px;
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.7;
}

/* ===== FOOTER ===== */
.footer {
    position: relative;
    z-index: 1;
    border-top: 1px solid var(--border-subtle);
    background: rgba(7, 8, 15, 0.8);
}

.footer-container {
    max-width: var(--container-max);
    margin: 0 auto;
    padding: var(--container-padding);
}

.footer-top {
    display: grid;
    grid-template-columns: 1.5fr 1fr 1fr 1fr;
    gap: 40px;
    padding: 60px 0 40px;
}

.footer-tagline {
    font-size: 0.9rem;
    color: var(--text-secondary);
    margin-top: 16px;
    line-height: 1.6;
    max-width: 280px;
}

.footer-links-group h4,
.footer-links-group .footer-group-title {
    font-family: var(--font-display);
    font-size: 0.85rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 16px;
    text-transform: uppercase;
    letter-spacing: 0.08em;
}

.footer-links-group a {
    display: block;
    font-size: 0.875rem;
    color: var(--text-secondary);
    padding: 6px 0;
    transition: var(--transition-base);
}

.footer-links-group a:hover {
    color: var(--accent-start);
    transform: translateX(4px);
}

.footer-bottom {
    border-top: 1px solid var(--border-subtle);
    padding: 24px 0;
    text-align: center;
}

.footer-bottom p {
    font-size: 0.8rem;
    color: var(--text-muted);
}

.footer-languages {
    padding: 0 0 36px;
}

.footer-languages .footer-group-title {
    margin-bottom: 14px;
}

.footer-language-links {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

.footer-language-links a {
    min-width: 42px;
    padding: 8px 10px;
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-sm);
    color: var(--text-secondary);
    background: var(--bg-glass);
    font-size: 0.75rem;
    font-weight: 700;
    line-height: 1;
    text-align: center;
}

.footer-language-links a:hover,
.footer-language-links a[aria-current="page"] {
    border-color: var(--border-accent);
    color: var(--text-primary);
    background: rgba(99, 102, 241, 0.1);
    transform: translateY(-1px);
}

[dir="rtl"] .how-calc-prose,
[dir="rtl"] .how-calc-bottom-note p {
    text-align: right;
}

[dir="rtl"] .footer-language-links {
    direction: ltr;
    justify-content: flex-end;
}

/* ===== BACK TO TOP ===== */
.back-to-top {
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 44px;
    height: 44px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--gradient-primary);
    border-radius: 50%;
    color: #fff;
    box-shadow: 0 4px 20px rgba(99, 102, 241, 0.3);
    opacity: 0;
    visibility: hidden;
    transform: translateY(10px);
    transition: var(--transition-base);
    z-index: 999;
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.back-to-top:hover {
    transform: translateY(-3px);
    box-shadow: 0 6px 30px rgba(99, 102, 241, 0.5);
}

/* ===== RESPONSIVE ===== */
@media (max-width: 1200px) {
    .calculator-layout {
        grid-template-columns: 1fr 1fr;
    }
    .calc-visual {
        grid-column: 1 / -1;
        grid-row: 1;
        position: static;
    }
    .calc-results {
        grid-column: 1 / -1;
    }
    .formulas-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    .how-calc-grid {
        grid-template-columns: repeat(3, 1fr);
    }
    .formula-ref-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 900px) {
    :root {
        --section-padding: 80px 0;
    }
    .nav-links {
        display: none;
    }
    .mobile-menu-btn {
        display: flex;
    }
    .hero-container {
        grid-template-columns: 1fr;
        text-align: center;
        gap: 40px;
    }
    .hero-description {
        margin: 0 auto 36px;
    }
    .hero-actions {
        justify-content: center;
    }
    .hero-stats {
        justify-content: center;
    }
    .hero-tank-container {
        width: 350px;
        height: 350px;
    }
    .steps-grid {
        flex-direction: column;
    }
    .step-connector {
        transform: rotate(90deg);
        width: 40px;
    }
    .calculator-layout {
        grid-template-columns: 1fr;
    }
    .calc-visual {
        grid-row: auto;
    }
    .features-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    .how-calc-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    .formula-ref-grid {
        grid-template-columns: 1fr;
    }
    .comparison-notes {
        grid-template-columns: 1fr;
    }
    .footer-top {
        grid-template-columns: 1fr 1fr;
        gap: 32px;
    }
}

@media (max-width: 600px) {
    :root {
        --container-padding: 0 20px;
        --section-padding: 64px 0;
    }
    .hero-title {
        font-size: 2rem;
    }
    .hero-actions {
        flex-direction: column;
        align-items: center;
    }
    .hero-stats {
        flex-direction: column;
        gap: 16px;
    }
    .hero-stat-divider {
        width: 40px;
        height: 1px;
    }
    .hero-tank-container {
        width: 280px;
        height: 280px;
    }
    .features-grid {
        grid-template-columns: 1fr;
    }
    .formulas-grid {
        grid-template-columns: 1fr;
    }
    .footer-top {
        grid-template-columns: 1fr;
    }
    .anatomy-canvas-wrap {
        padding: 16px;
    }
    .calculator-anatomy {
        margin-top: 48px;
    }
    .anatomy-selector {
        align-items: stretch;
    }
    .anatomy-btn {
        flex: 1;
        padding: 10px 12px;
    }
    .how-calc-grid {
        grid-template-columns: 1fr;
    }
    .how-calc-bottom-note {
        padding: 20px;
    }
    .formula-ref-conversion-note {
        padding: 20px;
    }
    .comparison-notes {
        grid-template-columns: 1fr;
    }
}

/* ===== SCROLL ANIMATIONS ===== */
.step-card,
.feature-card,
.formula-card,
.faq-item,
.how-calc-card,
.formula-ref-card {
    opacity: 0;
    transform: translateY(30px);
    transition: opacity 0.6s ease, transform 0.6s ease, background var(--transition-base), border-color var(--transition-base), box-shadow var(--transition-base);
}

.step-card.animate-in,
.feature-card.animate-in,
.formula-card.animate-in,
.faq-item.animate-in,
.how-calc-card.animate-in,
.formula-ref-card.animate-in {
    opacity: 1;
    transform: translateY(0);
}