:root {
    --primary-color: #4f46e5;
    --primary-hover: #4338ca;
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --text-main: #1e293b;
    --text-muted: #64748b;
    --border-color: #e2e8f0;
    --shadow: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --transition-speed: 0.3s;
}

[data-theme="dark"] {
    --primary-color: #818cf8;
    --primary-hover: #6366f1;
    --bg-color: #0f172a;
    --card-bg: #1e293b;
    --text-main: #f1f5f9;
    --text-muted: #94a3b8;
    --border-color: #334155;
    --shadow: 0 4px 6px -1px rgb(0 0 0 / 0.4), 0 2px 4px -2px rgb(0 0 0 / 0.4);
}

body {
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    transition: background-color var(--transition-speed) ease, color var(--transition-speed) ease;
}

.container {
    width: 100%;
    max-width: 600px;
    padding: 20px;
}

.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
    gap: 1rem;
}

.header h1 {
    margin: 0;
    text-align: left;
    font-weight: 700;
    font-size: 2rem;
    color: var(--text-main);
    transition: color var(--transition-speed) ease;
}

.theme-toggle {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    color: var(--text-main);
    cursor: pointer;
    width: 44px;
    height: 44px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.25rem;
    transition: all 0.2s ease;
    box-shadow: var(--shadow);
}

.theme-toggle:hover {
    transform: scale(1.1);
    border-color: var(--primary-color);
}

.converter-card {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: 1rem;
    box-shadow: var(--shadow);
    border: 1px solid var(--border-color);
    transition: background-color var(--transition-speed) ease, border-color var(--transition-speed) ease, box-shadow var(--transition-speed) ease;
}

.category-selector {
    margin-bottom: 2rem;
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.category-selector label {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-muted);
    transition: color var(--transition-speed) ease;
}

.category-selector select {
    padding: 0.75rem;
    border-radius: 0.5rem;
    border: 1px solid var(--border-color);
    font-size: 1rem;
    background: var(--card-bg);
    color: var(--text-main);
    cursor: pointer;
    outline: none;
    transition: border-color 0.2s, background-color var(--transition-speed) ease, color var(--transition-speed) ease;
}

.category-selector select:focus {
    border-color: var(--primary-color);
}

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

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

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

.field-wrapper {
    display: flex;
    gap: 0.5rem;
}

.field-wrapper input {
    flex: 1;
    padding: 0.75rem;
    border-radius: 0.5rem;
    border: 1px solid var(--border-color);
    font-size: 1rem;
    background: var(--card-bg);
    color: var(--text-main);
    outline: none;
    transition: border-color 0.2s, background-color var(--transition-speed) ease, color var(--transition-speed) ease;
}

.field-wrapper input:focus {
    border-color: var(--primary-color);
}

.field-wrapper select {
    padding: 0.75rem;
    border-radius: 0.5rem;
    border: 1px solid var(--border-color);
    font-size: 0.875rem;
    background: var(--card-bg);
    color: var(--text-main);
    cursor: pointer;
    outline: none;
    transition: border-color 0.2s, background-color var(--transition-speed) ease, color var(--transition-speed) ease;
}

.swap-button {
    display: flex;
    align-items: center;
    justify-content: center;
    height: 44px;
}

.swap-button button {
    width: 44px;
    height: 44px;
    border-radius: 50%;
    border: 1px solid var(--border-color);
    background: var(--card-bg);
    cursor: pointer;
    font-size: 1.25rem;
    transition: all 0.2s ease;
    color: var(--text-muted);
}

.swap-button button:hover {
    background: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
}

.formula-display {
    margin-top: 2rem;
    text-align: center;
    font-size: 0.875rem;
    color: var(--text-muted);
    font-style: italic;
    min-height: 1.25rem;
    transition: color var(--transition-speed) ease;
}

@media (max-width: 480px) {
    .conversion-grid {
        grid-template-columns: 1fr;
        gap: 1rem;
    }
    .swap-button {
        transform: rotate(90deg);
        margin: 0.5rem 0;
    }
}