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

:root {
    --primary-color: #4A90E2;
    --primary-hover: #357ABD;
    --secondary-color: #7B68EE;
    --success-color: #52C41A;
    --warning-color: #FAAD14;
    --danger-color: #FF4757;
    --text-primary: #2C3E50;
    --text-secondary: #718096;
    --bg-primary: #FFFFFF;
    --bg-secondary: #F7FAFC;
    --bg-tertiary: #EDF2F7;
    --border-color: #E2E8F0;
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.12);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.1);
    --radius: 12px;
    --radius-sm: 8px;
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

body.dark {
    --primary-color: #5A9FE8;
    --primary-hover: #4A8FD8;
    --secondary-color: #8B78FF;
    --text-primary: #F7FAFC;
    --text-secondary: #CBD5E0;
    --bg-primary: #1A202C;
    --bg-secondary: #2D3748;
    --bg-tertiary: #4A5568;
    --border-color: #4A5568;
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.3);
}

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

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

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

.header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
}

.logo-icon {
    font-size: 2rem;
}

.header-controls {
    display: flex;
    gap: 1rem;
    align-items: center;
}

.language-selector {
    padding: 0.5rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: var(--bg-primary);
    color: var(--text-primary);
    font-size: 0.9rem;
    cursor: pointer;
    transition: var(--transition);
}

.language-selector:hover {
    border-color: var(--primary-color);
}

.theme-toggle {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    border: 1px solid var(--border-color);
    background: var(--bg-primary);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
}

.theme-toggle:hover {
    transform: rotate(20deg);
    border-color: var(--primary-color);
}

.theme-icon {
    font-size: 1.2rem;
}

/* Main Content */
.main {
    padding: 2rem 0 4rem;
}

.intro {
    text-align: center;
    margin-bottom: 3rem;
}

.intro h2 {
    font-size: 2rem;
    margin-bottom: 0.5rem;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.intro p {
    color: var(--text-secondary);
    font-size: 1.1rem;
}

/* Converter Section */
.converter-section {
    background: var(--bg-primary);
    border-radius: var(--radius);
    padding: 2rem;
    box-shadow: var(--shadow-md);
    margin-bottom: 2rem;
}

.category-tabs {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 2rem;
    overflow-x: auto;
    padding-bottom: 0.5rem;
}

.tab-button {
    padding: 0.75rem 1.5rem;
    border: none;
    background: var(--bg-tertiary);
    color: var(--text-secondary);
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 0.95rem;
    font-weight: 500;
    white-space: nowrap;
    transition: var(--transition);
}

.tab-button:hover {
    background: var(--bg-secondary);
}

.tab-button.active {
    background: var(--primary-color);
    color: white;
}

/* Converter Panel */
.converter-panel {
    animation: fadeIn 0.3s ease;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

.converter-inputs {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    gap: 2rem;
    align-items: center;
    margin-bottom: 2rem;
}

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

.input-group label {
    font-weight: 600;
    color: var(--text-secondary);
    font-size: 0.9rem;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.input-row {
    display: flex;
    gap: 0.5rem;
}

.value-input {
    flex: 1;
    padding: 1rem;
    border: 2px solid var(--border-color);
    border-radius: var(--radius-sm);
    font-size: 1.1rem;
    background: var(--bg-primary);
    color: var(--text-primary);
    transition: var(--transition);
}

.value-input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(74, 144, 226, 0.1);
}

.value-input.result {
    background: var(--bg-secondary);
    font-weight: 600;
}

.unit-select {
    padding: 1rem;
    border: 2px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: var(--bg-primary);
    color: var(--text-primary);
    font-size: 1rem;
    cursor: pointer;
    transition: var(--transition);
    min-width: 150px;
}

.unit-select:hover {
    border-color: var(--primary-color);
}

.swap-button {
    width: 48px;
    height: 48px;
    border-radius: 50%;
    border: 2px solid var(--border-color);
    background: var(--bg-primary);
    color: var(--text-primary);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
}

.swap-button:hover {
    transform: rotate(180deg);
    border-color: var(--primary-color);
    background: var(--primary-color);
    color: white;
}

/* Converter Actions */
.converter-actions {
    display: flex;
    gap: 1rem;
    margin-bottom: 1.5rem;
}

.action-button {
    flex: 1;
    padding: 1rem;
    border: none;
    border-radius: var(--radius-sm);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
    background: var(--primary-color);
    color: white;
}

.action-button:hover {
    background: var(--primary-hover);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.action-button.secondary {
    background: var(--bg-tertiary);
    color: var(--text-primary);
}

.action-button.secondary:hover {
    background: var(--border-color);
}

/* Precision Control */
.precision-control {
    display: flex;
    align-items: center;
    gap: 1rem;
    padding: 1rem;
    background: var(--bg-secondary);
    border-radius: var(--radius-sm);
}

.precision-control label {
    font-weight: 500;
    color: var(--text-secondary);
}

.precision-slider {
    flex: 1;
    -webkit-appearance: none;
    height: 6px;
    border-radius: 3px;
    background: var(--border-color);
    outline: none;
}

.precision-slider::-webkit-slider-thumb {
    -webkit-appearance: none;
    width: 20px;
    height: 20px;
    border-radius: 50%;
    background: var(--primary-color);
    cursor: pointer;
    transition: var(--transition);
}

.precision-slider::-webkit-slider-thumb:hover {
    transform: scale(1.2);
}

#precisionValue {
    font-weight: 600;
    color: var(--primary-color);
    min-width: 30px;
    text-align: center;
}

/* History Section */
.history-section {
    background: var(--bg-primary);
    border-radius: var(--radius);
    padding: 2rem;
    box-shadow: var(--shadow-md);
    margin-bottom: 2rem;
}

.history-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1.5rem;
}

.history-header h3 {
    font-size: 1.3rem;
    color: var(--text-primary);
}

.clear-history-button {
    padding: 0.5rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: transparent;
    color: var(--text-secondary);
    font-size: 0.9rem;
    cursor: pointer;
    transition: var(--transition);
}

.clear-history-button:hover {
    border-color: var(--danger-color);
    color: var(--danger-color);
}

.history-list {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.history-item {
    padding: 1rem;
    background: var(--bg-secondary);
    border-radius: var(--radius-sm);
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: var(--transition);
}

.history-item:hover {
    transform: translateX(5px);
    box-shadow: var(--shadow-sm);
}

.history-category {
    padding: 0.25rem 0.75rem;
    background: var(--primary-color);
    color: white;
    border-radius: 20px;
    font-size: 0.85rem;
    font-weight: 500;
}

.history-conversion {
    color: var(--text-primary);
    font-weight: 500;
}

.history-empty {
    text-align: center;
    color: var(--text-secondary);
    padding: 2rem;
    font-style: italic;
}

/* Quick Convert Section */
.quick-convert-section {
    background: var(--bg-primary);
    border-radius: var(--radius);
    padding: 2rem;
    box-shadow: var(--shadow-md);
}

.quick-convert-section h3 {
    font-size: 1.3rem;
    color: var(--text-primary);
    margin-bottom: 1.5rem;
}

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

.quick-convert-button {
    padding: 1rem;
    border: 2px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: var(--bg-primary);
    color: var(--text-primary);
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
}

.quick-convert-button:hover {
    border-color: var(--primary-color);
    background: var(--primary-color);
    color: white;
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

/* Footer */
.footer {
    background: var(--bg-primary);
    border-top: 1px solid var(--border-color);
    padding: 2rem 0;
    text-align: center;
    margin-top: 4rem;
}

.footer p {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

/* Toast */
.toast {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    padding: 1rem 1.5rem;
    background: var(--success-color);
    color: white;
    border-radius: var(--radius-sm);
    box-shadow: var(--shadow-lg);
    opacity: 0;
    transform: translateY(20px);
    transition: var(--transition);
    pointer-events: none;
    font-weight: 500;
    z-index: 1000;
}

.toast.show {
    opacity: 1;
    transform: translateY(0);
}

/* Responsive Design */
@media (max-width: 768px) {
    .converter-inputs {
        grid-template-columns: 1fr;
        gap: 1rem;
    }
    
    .swap-button {
        align-self: center;
        transform: rotate(90deg);
    }
    
    .swap-button:hover {
        transform: rotate(270deg);
    }
    
    .category-tabs {
        justify-content: flex-start;
    }
    
    .quick-convert-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .header .container {
        flex-wrap: wrap;
        gap: 1rem;
    }
    
    .intro h2 {
        font-size: 1.5rem;
    }
    
    .converter-actions {
        flex-direction: column;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 15px;
    }
    
    .converter-section,
    .history-section,
    .quick-convert-section {
        padding: 1.5rem;
    }
    
    .quick-convert-grid {
        grid-template-columns: 1fr;
    }
    
    .category-tabs {
        gap: 0.25rem;
    }
    
    .tab-button {
        padding: 0.5rem 1rem;
        font-size: 0.85rem;
    }
}