/* ==========================================
   ConvertUnit Free — Stylesheet
   Same design system as Image / Document / Audio / Video Converters
   ========================================== */

/* ==========================================
   Design Tokens
   ========================================== */
:root {
    --font: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --blue-50:  #eff6ff;  --blue-100: #dbeafe;  --blue-200: #bfdbfe;
    --blue-300: #93c5fd;  --blue-400: #60a5fa;  --blue-500: #3b82f6;
    --blue-600: #2563eb;  --blue-700: #1d4ed8;  --blue-800: #1e40af;
    --blue-900: #1e3a8a;
    --gray-50:  #f8fafc;  --gray-100: #f1f5f9;  --gray-200: #e2e8f0;
    --gray-300: #cbd5e1;  --gray-400: #94a3b8;  --gray-500: #64748b;
    --gray-600: #475569;  --gray-700: #334155;  --gray-800: #1e293b;
    --gray-900: #0f172a;
    --green-600: #16a34a;
    --radius-sm: 6px;  --radius-md: 8px;  --radius-lg: 12px;
    --radius-xl: 16px; --radius-2xl: 24px; --radius-full: 9999px;
    --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
    --shadow-md: 0 4px 12px rgba(0,0,0,0.08);
    --shadow-lg: 0 8px 30px rgba(0,0,0,0.08);
    --shadow-xl: 0 20px 60px rgba(0,0,0,0.1);
    --transition: 0.2s ease;
}

/* Reset */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

body {
    font-family: var(--font);
    background: var(--gray-50);
    color: var(--gray-700);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

a { text-decoration: none; color: inherit; }

.container { max-width: 1080px; margin: 0 auto; padding: 0 24px; }

.gradient-text {
    background: linear-gradient(135deg, var(--blue-500), var(--blue-700));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

/* ==========================================
   Header
   ========================================== */
.header {
    position: sticky; top: 0; z-index: 100;
    background: rgba(255,255,255,0.85);
    backdrop-filter: blur(16px);
    border-bottom: 1px solid var(--gray-100);
}

.header-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 64px;
}

.logo {
    display: flex;
    align-items: center;
    gap: 10px;
    font-size: 1.15rem;
    font-weight: 700;
}

.logo-img {
    width: 36px;
    height: 36px;
    border-radius: var(--radius-md);
}

.logo-text { color: var(--gray-800); }

.header-nav {
    display: flex;
    gap: 28px;
    font-size: 0.88rem;
    font-weight: 500;
}

.header-nav a {
    color: var(--gray-500);
    transition: color var(--transition);
}

.header-nav a:hover { color: var(--blue-600); }

/* ==========================================
   Hero
   ========================================== */
.hero {
    padding: 80px 0 40px;
    text-align: center;
}

.hero h1 {
    font-size: 2.8rem;
    font-weight: 800;
    line-height: 1.15;
    color: var(--gray-900);
    letter-spacing: -0.025em;
}

.hero-subtitle {
    margin-top: 16px;
    font-size: 1.12rem;
    color: var(--gray-500);
    max-width: 620px;
    margin-left: auto;
    margin-right: auto;
}

/* ==========================================
   Converter Section
   ========================================== */
.converter-section {
    padding: 20px 0 60px;
}

.converter-card {
    background: #fff;
    border: 1px solid var(--gray-200);
    border-radius: var(--radius-2xl);
    padding: 40px;
    box-shadow: var(--shadow-lg);
}

/* Category Tabs */
.category-tabs {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    margin-bottom: 32px;
    justify-content: center;
}

.category-tab {
    padding: 8px 18px;
    border: 1px solid var(--gray-200);
    border-radius: var(--radius-full);
    background: var(--gray-50);
    color: var(--gray-600);
    font-size: 0.88rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition);
    font-family: var(--font);
}

.category-tab:hover {
    border-color: var(--blue-300);
    background: var(--blue-50);
    color: var(--blue-600);
}

.category-tab.active {
    background: var(--blue-600);
    color: #fff;
    border-color: var(--blue-600);
}

/* Converter Body */
.converter-body {
    display: flex;
    align-items: center;
    gap: 24px;
}

.converter-input-group {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.converter-input-group label {
    font-size: 0.82rem;
    font-weight: 600;
    color: var(--gray-500);
    text-transform: uppercase;
    letter-spacing: 0.04em;
}

.converter-input-group input {
    width: 100%;
    padding: 14px 16px;
    font-size: 1.6rem;
    font-weight: 700;
    font-family: var(--font);
    color: var(--gray-900);
    border: 1px solid var(--gray-200);
    border-radius: var(--radius-lg);
    background: var(--gray-50);
    outline: none;
    transition: border-color var(--transition), box-shadow var(--transition);
}

.converter-input-group input:focus {
    border-color: var(--blue-400);
    box-shadow: 0 0 0 3px rgba(59,130,246,0.15);
}

.converter-input-group select {
    width: 100%;
    padding: 10px 14px;
    font-size: 0.92rem;
    font-weight: 500;
    font-family: var(--font);
    color: var(--gray-700);
    border: 1px solid var(--gray-200);
    border-radius: var(--radius-md);
    background: #fff;
    cursor: pointer;
    outline: none;
    transition: border-color var(--transition);
}

.converter-input-group select:focus {
    border-color: var(--blue-400);
}

/* Swap Button */
.swap-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 48px;
    height: 48px;
    border: 1px solid var(--gray-200);
    border-radius: var(--radius-full);
    background: #fff;
    cursor: pointer;
    color: var(--gray-500);
    transition: all var(--transition);
    flex-shrink: 0;
    font-family: var(--font);
}

.swap-btn:hover {
    border-color: var(--blue-400);
    color: var(--blue-600);
    background: var(--blue-50);
}

/* Formula Display */
.formula-display {
    margin-top: 20px;
    padding: 14px 20px;
    background: var(--blue-50);
    border: 1px solid var(--blue-100);
    border-radius: var(--radius-lg);
    font-size: 0.9rem;
    color: var(--blue-800);
    text-align: center;
}

.formula-display strong {
    font-weight: 700;
}

/* Quick Values Grid */
.quick-values {
    margin-top: 24px;
}

.quick-values h3 {
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--gray-500);
    text-transform: uppercase;
    letter-spacing: 0.04em;
    margin-bottom: 12px;
}

.quick-values-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
    gap: 8px;
}

.quick-value-item {
    display: flex;
    justify-content: space-between;
    padding: 10px 14px;
    background: var(--gray-50);
    border: 1px solid var(--gray-100);
    border-radius: var(--radius-md);
    font-size: 0.88rem;
}

.quick-value-item .qv-from {
    color: var(--gray-500);
    font-weight: 500;
}

.quick-value-item .qv-to {
    color: var(--gray-800);
    font-weight: 600;
}

/* ==========================================
   Conversions Section
   ========================================== */
.conversions-section {
    padding: 60px 0;
    text-align: center;
}

.conversions-section h2 {
    font-size: 2rem;
    font-weight: 800;
    color: var(--gray-900);
    letter-spacing: -0.02em;
}

.section-subtitle {
    margin-top: 10px;
    color: var(--gray-500);
    font-size: 1.05rem;
    margin-bottom: 40px;
}

.conversions-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
    gap: 10px;
    text-align: center;
}

.conversion-item {
    padding: 12px 8px;
    background: var(--blue-50);
    border: 1px solid var(--blue-100);
    border-radius: var(--radius-md);
    font-size: 0.88rem;
    font-weight: 600;
    color: var(--blue-700);
    transition: transform var(--transition), box-shadow var(--transition);
}

.conversion-item:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-sm);
}

/* ==========================================
   Features Section
   ========================================== */
.features-section {
    padding: 60px 0 80px;
    text-align: center;
}

.features-section h2 {
    font-size: 2rem;
    font-weight: 800;
    color: var(--gray-900);
    letter-spacing: -0.02em;
}

.features-illustration {
    max-width: 680px;
    margin: 36px auto 48px;
}

.features-illustration svg {
    width: 100%;
    height: auto;
}

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

.feature-card {
    padding: 28px 24px;
    background: var(--gray-50);
    border: 1px solid var(--gray-200);
    border-radius: var(--radius-xl);
    transition: transform var(--transition), box-shadow var(--transition);
}

.feature-card:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-md);
}

.feature-card h3 {
    font-size: 1.05rem;
    font-weight: 700;
    color: var(--gray-800);
    margin-bottom: 8px;
}

.feature-card p {
    font-size: 0.9rem;
    color: var(--gray-500);
    line-height: 1.6;
}

/* ==========================================
   Footer
   ========================================== */
.footer {
    border-top: 1px solid var(--gray-100);
    padding: 32px 0;
    text-align: center;
}

.footer-inner p {
    font-size: 0.85rem;
    color: var(--gray-400);
}

.footer-sub {
    margin-top: 6px;
    font-size: 0.78rem;
    color: var(--gray-300);
}

/* ==========================================
   Buttons
   ========================================== */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 10px 22px;
    border: none;
    border-radius: var(--radius-md);
    font-family: var(--font);
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition);
}

.btn-primary {
    background: var(--blue-600);
    color: #fff;
}

.btn-primary:hover {
    background: var(--blue-700);
    box-shadow: var(--shadow-md);
}

.btn-primary:disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

.btn-outline {
    background: #fff;
    color: var(--blue-600);
    border: 1px solid var(--blue-200);
}

.btn-outline:hover {
    background: var(--blue-50);
}

.btn-ghost {
    background: transparent;
    color: var(--gray-500);
}

.btn-ghost:hover {
    background: var(--gray-100);
    color: var(--gray-700);
}

/* ==========================================
   Category Badge Colors
   ========================================== */
.category-badge {
    display: inline-block;
    padding: 3px 10px;
    border-radius: var(--radius-full);
    font-size: 0.72rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.04em;
}

.category-badge.length      { background: #dbeafe; color: #1d4ed8; }
.category-badge.weight      { background: #dcfce7; color: #16a34a; }
.category-badge.temperature { background: #fee2e2; color: #dc2626; }
.category-badge.area        { background: #f3e8ff; color: #9333ea; }
.category-badge.volume      { background: #fef3c7; color: #d97706; }
.category-badge.speed       { background: #cffafe; color: #0891b2; }
.category-badge.time        { background: #fce7f3; color: #db2777; }
.category-badge.data        { background: #e0e7ff; color: #4f46e5; }
.category-badge.pressure    { background: #f1f5f9; color: #475569; }
.category-badge.energy      { background: #fef9c3; color: #a16207; }

/* ==========================================
   Responsive
   ========================================== */
@media (max-width: 768px) {
    .hero h1 { font-size: 2rem; }
    .converter-card { padding: 24px; }
    .converter-body { flex-direction: column; }
    .swap-btn { transform: rotate(90deg); }
    .features-grid { grid-template-columns: 1fr; }
    .conversions-grid { grid-template-columns: repeat(2, 1fr); }
    .quick-values-grid { grid-template-columns: 1fr; }
    .category-tabs { gap: 6px; }
    .category-tab { padding: 6px 14px; font-size: 0.82rem; }
}

@media (max-width: 480px) {
    .hero h1 { font-size: 1.6rem; }
    .hero-subtitle { font-size: 0.95rem; }
    .converter-card { padding: 16px; }
    .converter-input-group input { font-size: 1.2rem; padding: 12px 14px; }
    .header-nav { gap: 16px; font-size: 0.82rem; }
}