:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --heading-color: #0f172a;
    --text-color: #334155;
    --text-muted: #64748b;
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --border-color: #e2e8f0;
    --success-color: #16a34a;
    --danger-color: #dc2626;
    --warning-color: #d97706;
    --radius: 0.5rem;
    --radius-lg: 1rem;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.06), 0 1px 2px rgba(0, 0, 0, 0.04);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.06), 0 2px 4px rgba(0, 0, 0, 0.04);
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    color: var(--text-color);
    background-color: var(--bg-color);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

/* Header */
.header {
    position: sticky;
    top: 0;
    z-index: 100;
    background: var(--card-bg);
    border-bottom: 1px solid var(--border-color);
}

.header-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 3.5rem;
}

.logo {
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--heading-color);
    text-decoration: none;
}

.nav-link {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--primary-color);
    text-decoration: none;
    transition: opacity 0.15s;
}

.nav-link:hover {
    opacity: 0.8;
}

/* Hero */
.hero {
    padding: 3rem 0 1.5rem;
    text-align: center;
}

.hero h1 {
    font-size: 2rem;
    font-weight: 700;
    color: var(--heading-color);
    margin-bottom: 0.5rem;
}

.hero-subtitle {
    font-size: 1rem;
    color: var(--text-muted);
    max-width: 600px;
    margin: 0 auto;
}

/* Cards */
.card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 1.5rem;
    box-shadow: var(--shadow);
}

/* Experiment title */
.experiment-title-card {
    margin-bottom: 1rem;
}

/* Variant cards */
.variant-card {
    margin-bottom: 1rem;
}

.variant-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 1rem;
}

.variant-title {
    font-size: 1rem;
    font-weight: 600;
    color: var(--heading-color);
}

.btn-remove {
    background: none;
    border: 1px solid var(--border-color);
    color: var(--text-muted);
    font-size: 0.8rem;
    padding: 0.25rem 0.75rem;
    border-radius: var(--radius);
    cursor: pointer;
    transition: color 0.15s, border-color 0.15s;
}

.btn-remove:hover {
    color: var(--danger-color);
    border-color: var(--danger-color);
}

/* Inputs */
.input-label {
    display: block;
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-muted);
    margin-bottom: 0.35rem;
    text-transform: uppercase;
    letter-spacing: 0.03em;
}

.input {
    width: 100%;
    padding: 0.6rem 0.75rem;
    font-size: 0.95rem;
    font-family: inherit;
    color: var(--heading-color);
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    transition: border-color 0.15s, box-shadow 0.15s;
    outline: none;
}

.input:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.12);
}

.input::placeholder {
    color: var(--text-muted);
    opacity: 0.6;
}

.inputs-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
}

/* Results area */
.results-area {
    margin-top: 1rem;
}

.results-area:empty {
    display: none;
}

.results-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
    gap: 0.75rem;
}

.result-item {
    padding: 0.75rem;
    background: var(--bg-color);
    border-radius: var(--radius);
    text-align: center;
}

.result-label {
    font-size: 0.7rem;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.04em;
    margin-bottom: 0.25rem;
}

.result-value {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--heading-color);
}

.result-value.positive {
    color: var(--success-color);
}

.result-value.negative {
    color: var(--danger-color);
}

/* Significance badge */
.badge {
    display: inline-block;
    padding: 0.3rem 0.75rem;
    border-radius: 999px;
    font-size: 0.8rem;
    font-weight: 600;
}

.badge-significant {
    background: #dcfce7;
    color: var(--success-color);
}

.badge-not-significant {
    background: #fef3c7;
    color: var(--warning-color);
}

/* Low data warning */
.low-data-warning {
    margin-top: 1.25rem;
    padding: 0.75rem 1rem;
    background: #fef3c7;
    border: 1px solid #fde68a;
    border-radius: var(--radius);
    font-size: 0.85rem;
    color: #92400e;
    line-height: 1.5;
}

/* Action buttons */
.actions {
    display: flex;
    gap: 0.75rem;
    margin-top: 0.5rem;
}

.btn {
    padding: 0.6rem 1.25rem;
    font-size: 0.9rem;
    font-weight: 600;
    font-family: inherit;
    border: none;
    border-radius: var(--radius);
    cursor: pointer;
    transition: background 0.15s, opacity 0.15s;
}

.btn-primary {
    background: var(--primary-color);
    color: #ffffff;
}

.btn-primary:hover {
    background: var(--primary-hover);
}

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

.btn-secondary:hover {
    background: var(--bg-color);
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Footer */
.footer {
    text-align: center;
    padding: 2.5rem 0;
    margin-top: 2rem;
    color: var(--text-muted);
    font-size: 0.85rem;
    border-top: 1px solid var(--border-color);
}

/* Responsive */
@media (max-width: 768px) {
    .hero h1 {
        font-size: 1.5rem;
    }

    .inputs-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 480px) {
    .results-grid {
        grid-template-columns: 1fr 1fr;
    }

    .actions {
        flex-direction: column;
    }
}