/* CSS Variables */
:root {
    --bg-primary: #0f1117;
    --bg-secondary: #1a1d24;
    --bg-card: #22262f;
    --bg-hover: #2a2f3a;
    --text-primary: #f0f2f5;
    --text-secondary: #a0a6b1;
    --text-muted: #6b7280;
    --accent-primary: #3b82f6;
    --accent-green: #22c55e;
    --accent-yellow: #eab308;
    --accent-orange: #f97316;
    --accent-red: #ef4444;
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --transition-fast: 150ms ease;
}

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

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

.app {
    max-width: 500px;
    margin: 0 auto;
    padding: 24px;
}

.back-link {
    display: inline-block;
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 0.9rem;
    margin-bottom: 24px;
    transition: var(--transition-fast);
}
.back-link:hover { color: var(--accent-primary); }

.header { text-align: center; margin-bottom: 32px; }
.title { font-size: 2rem; font-weight: 700; margin-bottom: 8px; }
.subtitle { color: var(--text-secondary); }

.calculator {
    background: var(--bg-card);
    border-radius: var(--radius-lg);
    padding: 24px;
    margin-bottom: 32px;
}

/* Unit Toggle */
.unit-toggle {
    display: flex;
    gap: 8px;
    margin-bottom: 24px;
}
.unit-btn {
    flex: 1;
    padding: 12px;
    background: var(--bg-secondary);
    border: 1px solid var(--bg-hover);
    border-radius: var(--radius-sm);
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition-fast);
}
.unit-btn:hover { border-color: var(--accent-primary); }
.unit-btn.active {
    background: var(--accent-primary);
    border-color: var(--accent-primary);
    color: white;
}

.input-section.hidden { display: none; }

.input-group { margin-bottom: 16px; }
.input-group label {
    display: block;
    font-size: 0.9rem;
    font-weight: 500;
    color: var(--text-secondary);
    margin-bottom: 8px;
}

.height-inputs {
    display: flex;
    gap: 12px;
}
.height-inputs .input-wrapper { flex: 1; }

.input-wrapper {
    position: relative;
    display: flex;
    align-items: center;
}
.input-wrapper .suffix {
    position: absolute;
    right: 14px;
    color: var(--text-muted);
    font-size: 0.9rem;
}

input[type="number"] {
    width: 100%;
    padding: 14px 50px 14px 16px;
    background: var(--bg-secondary);
    border: 1px solid var(--bg-hover);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    font-size: 1.1rem;
    transition: var(--transition-fast);
}
input[type="number"]:focus {
    outline: none;
    border-color: var(--accent-primary);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.2);
}

/* BMI Display */
.results-section { margin-top: 24px; }

.bmi-display {
    text-align: center;
    padding: 24px;
    background: var(--bg-secondary);
    border-radius: var(--radius-md);
    margin-bottom: 20px;
}
.bmi-label {
    display: block;
    font-size: 0.85rem;
    color: var(--text-muted);
    margin-bottom: 4px;
}
.bmi-value {
    display: block;
    font-size: 4rem;
    font-weight: 800;
    line-height: 1;
    margin-bottom: 8px;
}
.bmi-value.underweight { color: var(--accent-primary); }
.bmi-value.normal { color: var(--accent-green); }
.bmi-value.overweight { color: var(--accent-yellow); }
.bmi-value.obese { color: var(--accent-orange); }
.bmi-value.obese-severe { color: var(--accent-red); }

.bmi-category {
    display: inline-block;
    padding: 6px 16px;
    border-radius: 20px;
    font-size: 0.9rem;
    font-weight: 600;
}
.bmi-category.underweight { background: rgba(59, 130, 246, 0.2); color: var(--accent-primary); }
.bmi-category.normal { background: rgba(34, 197, 94, 0.2); color: var(--accent-green); }
.bmi-category.overweight { background: rgba(234, 179, 8, 0.2); color: var(--accent-yellow); }
.bmi-category.obese { background: rgba(249, 115, 22, 0.2); color: var(--accent-orange); }
.bmi-category.obese-severe { background: rgba(239, 68, 68, 0.2); color: var(--accent-red); }

/* BMI Scale */
.bmi-scale { margin-bottom: 20px; }
.scale-bar {
    height: 12px;
    border-radius: 6px;
    background: linear-gradient(to right,
        var(--accent-primary) 0%,
        var(--accent-green) 15%,
        var(--accent-green) 40%,
        var(--accent-yellow) 55%,
        var(--accent-orange) 70%,
        var(--accent-red) 100%
    );
    position: relative;
    margin-bottom: 8px;
}
.scale-marker {
    position: absolute;
    top: -4px;
    width: 20px;
    height: 20px;
    background: white;
    border: 3px solid var(--bg-primary);
    border-radius: 50%;
    transform: translateX(-50%);
    box-shadow: 0 2px 8px rgba(0,0,0,0.3);
    transition: left 0.3s ease;
}
.scale-labels {
    display: flex;
    justify-content: space-between;
    font-size: 0.7rem;
    color: var(--text-muted);
    margin-bottom: 4px;
}
.scale-categories {
    display: flex;
    justify-content: space-between;
    font-size: 0.65rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

/* Healthy Range */
.healthy-range {
    background: var(--bg-secondary);
    padding: 16px;
    border-radius: var(--radius-md);
    text-align: center;
}
.healthy-range h3 {
    font-size: 0.85rem;
    color: var(--text-muted);
    margin-bottom: 8px;
    font-weight: 500;
}
.healthy-range p {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--accent-green);
}

/* BMI Chart */
.bmi-chart { margin-bottom: 32px; }
.bmi-chart h2 {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: 16px;
}
.chart-grid { display: flex; flex-direction: column; gap: 6px; }
.chart-row {
    display: flex;
    justify-content: space-between;
    padding: 12px 16px;
    border-radius: var(--radius-sm);
    font-size: 0.9rem;
}
.chart-category { font-weight: 600; }
.chart-range { color: var(--text-muted); }
.chart-row.underweight { background: rgba(59, 130, 246, 0.15); }
.chart-row.normal { background: rgba(34, 197, 94, 0.15); }
.chart-row.overweight { background: rgba(234, 179, 8, 0.15); }
.chart-row.obese1 { background: rgba(249, 115, 22, 0.15); }
.chart-row.obese2 { background: rgba(239, 68, 68, 0.12); }
.chart-row.obese3 { background: rgba(239, 68, 68, 0.2); }

/* FAQ */
.faq-section { margin-bottom: 32px; }
.faq-title { font-size: 1.25rem; margin-bottom: 16px; }
.faq-item {
    background: var(--bg-card);
    border-radius: var(--radius-md);
    margin-bottom: 8px;
    overflow: hidden;
}
.faq-question {
    width: 100%;
    padding: 16px;
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    cursor: pointer;
    list-style: none;
}
.faq-question::-webkit-details-marker { display: none; }
.faq-question:hover { background: var(--bg-hover); }
.faq-answer { padding: 0 16px 16px; color: var(--text-secondary); }
.faq-answer ul { margin-left: 20px; margin-top: 8px; }
.faq-answer li { margin-bottom: 4px; }

/* Footer */
.footer { text-align: center; color: var(--text-muted); font-size: 0.85rem; }
.disclaimer { margin: 8px 0; font-size: 0.8rem; }
.related-tools { margin-top: 8px; }
.related-tools a { color: var(--accent-primary); text-decoration: none; }
.related-tools a:hover { text-decoration: underline; }

@media (max-width: 400px) {
    .bmi-value { font-size: 3rem; }
}