/* CSS Variables */
:root {
    --primary-color: #667eea;
    --primary-dark: #5a67d8;
    --secondary-color: #764ba2;
    --accent-color: #f093fb;
    --success-color: #48bb78;
    --danger-color: #f56565;
    
    --bg-color: #f7fafc;
    --card-bg: #ffffff;
    --text-color: #2d3748;
    --text-muted: #718096;
    --border-color: #e2e8f0;
    
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
    
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;
    
    --transition: all 0.3s ease;
}

[data-theme="dark"] {
    --bg-color: #1a202c;
    --card-bg: #2d3748;
    --text-color: #f7fafc;
    --text-muted: #a0aec0;
    --border-color: #4a5568;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    min-height: 100vh;
    transition: var(--transition);
}

.container { max-width: 900px; margin: 0 auto; padding: 2rem 1rem; }

header { text-align: center; margin-bottom: 2rem; }

header h1 {
    font-size: 2.5rem;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 0.5rem;
}

.subtitle { color: var(--text-muted); font-size: 1.1rem; }

/* Category Tabs */
.category-tabs {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    justify-content: center;
    margin-bottom: 1.5rem;
}

.tab-btn {
    padding: 0.6rem 1rem;
    background: var(--card-bg);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-lg);
    font-size: 0.9rem;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
    color: var(--text-color);
}

.tab-btn:hover { border-color: var(--primary-color); color: var(--primary-color); }

.tab-btn.active {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    border-color: transparent;
}

/* Converter Card */
.converter-card {
    background: var(--card-bg);
    border-radius: var(--radius-xl);
    padding: 2rem;
    box-shadow: var(--shadow-lg);
    margin-bottom: 2rem;
}

.converter-grid {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    gap: 1rem;
    align-items: end;
    margin-bottom: 1.5rem;
}

@media (max-width: 600px) {
    .converter-grid { grid-template-columns: 1fr; }
    .swap-btn { justify-self: center; transform: rotate(90deg); }
}

.input-group { display: flex; flex-direction: column; gap: 0.5rem; }

.input-group label {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-muted);
}

.input-group input, .input-group select {
    padding: 0.75rem 1rem;
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    font-size: 1.1rem;
    background: var(--bg-color);
    color: var(--text-color);
    transition: var(--transition);
}

.input-group input:focus, .input-group select:focus {
    outline: none;
    border-color: var(--primary-color);
}

.input-group input[readonly] {
    background: var(--card-bg);
    font-weight: 600;
    color: var(--primary-color);
}

.swap-btn {
    width: 50px;
    height: 50px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    transition: var(--transition);
    align-self: center;
}

.swap-btn:hover { transform: scale(1.1); }

.formula-display {
    text-align: center;
    padding: 1rem;
    background: var(--bg-color);
    border-radius: var(--radius-md);
    font-family: 'SF Mono', monospace;
    font-size: 0.95rem;
    color: var(--text-muted);
    margin-bottom: 1rem;
}

.copy-btn {
    display: block;
    width: 100%;
    padding: 0.875rem;
    background: var(--success-color);
    color: white;
    border: none;
    border-radius: var(--radius-lg);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
}

.copy-btn:hover { opacity: 0.9; }
.copy-btn.copied { background: var(--primary-color); }

/* Quick Conversions */
.quick-conversions {
    background: var(--card-bg);
    border-radius: var(--radius-xl);
    padding: 1.5rem;
    margin-bottom: 2rem;
    box-shadow: var(--shadow-md);
}

.quick-conversions h2 { font-size: 1.25rem; margin-bottom: 1rem; text-align: center; }

.quick-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 0.75rem;
}

.quick-item {
    padding: 0.75rem;
    background: var(--bg-color);
    border-radius: var(--radius-md);
    text-align: center;
    cursor: pointer;
    transition: var(--transition);
    border: 2px solid transparent;
}

.quick-item:hover { border-color: var(--primary-color); }

.quick-item .value { font-weight: 700; color: var(--primary-color); }
.quick-item .units { font-size: 0.85rem; color: var(--text-muted); }

/* Conversion Table */
.conversion-table-section {
    background: var(--card-bg);
    border-radius: var(--radius-xl);
    padding: 1.5rem;
    margin-bottom: 2rem;
    box-shadow: var(--shadow-md);
}

.conversion-table-section h2 { font-size: 1.25rem; margin-bottom: 1rem; text-align: center; }

.table-wrapper { overflow-x: auto; }

table { width: 100%; border-collapse: collapse; font-size: 0.9rem; }

th, td {
    padding: 0.75rem;
    text-align: center;
    border-bottom: 1px solid var(--border-color);
}

th {
    background: var(--bg-color);
    font-weight: 600;
    color: var(--text-muted);
}

tr:hover td { background: var(--bg-color); }

/* Trust Badges */
.trust-badges {
    display: flex;
    justify-content: center;
    gap: 1.5rem;
    flex-wrap: wrap;
    margin-bottom: 3rem;
}

.badge {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 1rem;
    background: var(--card-bg);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
}

.badge-icon { font-size: 1.25rem; }
.badge-text { font-size: 0.875rem; font-weight: 500; color: var(--text-muted); }

/* Features */
.features { margin-bottom: 3rem; }
.features h2 { text-align: center; font-size: 1.75rem; margin-bottom: 1.5rem; }

.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
}

.feature-card {
    background: var(--card-bg);
    border-radius: var(--radius-lg);
    padding: 1.5rem;
    box-shadow: var(--shadow-sm);
    text-align: center;
    transition: var(--transition);
}

.feature-card:hover { transform: translateY(-4px); box-shadow: var(--shadow-md); }
.feature-icon { font-size: 2.5rem; margin-bottom: 1rem; }
.feature-card h3 { font-size: 1.1rem; margin-bottom: 0.5rem; }
.feature-card p { font-size: 0.9rem; color: var(--text-muted); }

/* FAQ */
.faq-section { margin-bottom: 3rem; }
.faq-section h2 { text-align: center; font-size: 1.75rem; margin-bottom: 1.5rem; }
.faq-list { display: flex; flex-direction: column; gap: 0.75rem; }

.faq-item {
    background: var(--card-bg);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    overflow: hidden;
}

.faq-question {
    width: 100%;
    padding: 1rem 1.25rem;
    text-align: left;
    background: none;
    border: none;
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-color);
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.faq-question::after { content: '+'; font-size: 1.5rem; color: var(--primary-color); transition: var(--transition); }
.faq-item.active .faq-question::after { transform: rotate(45deg); }
.faq-question:hover { color: var(--primary-color); }

.faq-answer { max-height: 0; overflow: hidden; transition: max-height 0.3s ease; }
.faq-item.active .faq-answer { max-height: 500px; }
.faq-answer p { padding: 0 1.25rem 1rem; color: var(--text-muted); line-height: 1.7; }

/* Footer */
footer { text-align: center; padding: 2rem 1rem; color: var(--text-muted); font-size: 0.9rem; }

/* Theme Toggle */
.theme-toggle {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    width: 50px;
    height: 50px;
    border-radius: 50%;
    background: var(--card-bg);
    border: 2px solid var(--border-color);
    box-shadow: var(--shadow-lg);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
    z-index: 1000;
}

.theme-toggle:hover { transform: scale(1.1); border-color: var(--primary-color); }
.theme-icon { font-size: 1.5rem; }