:root {
    --primary: #4f46e5;
    --primary-hover: #4338ca;
    --bg: #f8fafc;
    --card-bg: #ffffff;
    --text-main: #1e293b;
    --text-muted: #64748b;
    --border: #e2e8f0;
    --accent: #f1f5f9;
    --shadow: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --radius: 12px;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    background-color: var(--bg);
    color: var(--text-main);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 20px;
}

.app-container {
    width: 100%;
    max-width: 500px;
    display: flex;
    flex-direction: column;
    gap: 2rem;
}

header {
    text-align: center;
}

header h1 {
    font-size: 2rem;
    font-weight: 700;
    color: var(--text-main);
    margin-bottom: 0.5rem;
}

header p {
    color: var(--text-muted);
    font-size: 1rem;
}

.converter-card {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    border: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    gap: 2rem;
}

.category-section {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.category-section label {
    font-weight: 600;
    font-size: 0.875rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.025em;
}

.category-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(80px, 1fr));
    gap: 0.5rem;
}

.category-btn {
    padding: 0.6rem;
    border: 1px solid var(--border);
    background: var(--card-bg);
    border-radius: 8px;
    cursor: pointer;
    font-size: 0.875rem;
    font-weight: 500;
    transition: all 0.2s ease;
    color: var(--text-muted);
}

.category-btn:hover {
    background: var(--accent);
    border-color: var(--primary);
}

.category-btn.active {
    background: var(--primary);
    color: white;
    border-color: var(--primary);
}

.conversion-interface {
    display: flex;
    align-items: center;
    gap: 1rem;
    position: relative;
}

.input-group {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.field {
    display: flex;
    flex-direction: column;
    gap: 0.4rem;
}

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

select, input {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border);
    border-radius: 8px;
    font-size: 1rem;
    font-family: inherit;
    transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

select:focus, input:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
}

.swap-container {
    display: flex;
    align-items: center;
    justify-content: center;
}

#swapUnits {
    background: var(--accent);
    border: 1px solid var(--border);
    width: 40px;
    height: 40px;
    border-radius: 50%;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-muted);
    transition: all 0.2s ease;
}

#swapUnits:hover {
    background: var(--border);
    color: var(--primary);
    transform: rotate(180deg);
}

.result-display {
    background: var(--accent);
    padding: 1rem;
    border-radius: 8px;
    text-align: center;
    font-weight: 600;
    font-size: 1.125rem;
    color: var(--primary);
    border: 1px dashed var(--border);
}

footer {
    text-align: center;
    color: var(--text-muted);
    font-size: 0.875rem;
}

.mobile-only {
    display: none;
}

@media (max-width: 480px) {
    .category-grid {
        display: none;
    }
    .mobile-only {
        display: block;
    }
    .conversion-interface {
        flex-direction: column;
    }
    .swap-container {
        transform: rotate(90deg);
    }
}