:root {
    --transition: all 0.3s ease;
}

.light-theme {
    --bg-primary: #ffffff;
    --bg-secondary: #f8fafc;
    --bg-tertiary: #e2e8f0;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --accent-primary: #3b82f6;
    --accent-hover: #2563eb;
    --border: #e2e8f0;
    --shadow: rgba(0, 0, 0, 0.1);
    --row-a: #ffffff;
    --row-b: #f8fafc;
    --success: #22c55e;
    --danger: #ef4444;
    --warning: #f59e0b;
}

.dark-theme {
    --bg-primary: #0f172a;
    --bg-secondary: #1e293b;
    --bg-tertiary: #334155;
    --text-primary: #f1f5f9;
    --text-secondary: #94a3b8;
    --accent-primary: #60a5fa;
    --accent-hover: #3b82f6;
    --border: #334155;
    --shadow: rgba(0, 0, 0, 0.3);
    --row-a: #1e293b;
    --row-b: #334155;
    --success: #10b981;
    --danger: #f87171;
    --warning: #fbbf24;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    transition: var(--transition);
}

.container {
    max-width: 800px;
    margin: 0 auto;
    padding: 20px;
    min-height: 100vh;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 30px;
    padding-bottom: 20px;
    border-bottom: 2px solid var(--border);
}

h1 {
    color: var(--accent-primary);
    font-size: 2rem;
    font-weight: 700;
}

.controls {
    display: flex;
    gap: 10px;
    align-items: center;
}

.btn-icon {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 8px 12px;
    cursor: pointer;
    font-size: 1.2rem;
    transition: var(--transition);
}

.btn-icon:hover {
    background: var(--bg-tertiary);
}

.btn-primary {
    background: var(--accent-primary);
    color: white;
    border: none;
    border-radius: 8px;
    padding: 10px 20px;
    cursor: pointer;
    font-weight: 600;
    transition: var(--transition);
}

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

.btn-secondary {
    background: var(--bg-secondary);
    color: var(--text-primary);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 8px 16px;
    cursor: pointer;
    font-weight: 500;
    transition: var(--transition);
}

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

.btn-danger {
    background: var(--danger);
    color: white;
    border: none;
    border-radius: 6px;
    padding: 6px 12px;
    cursor: pointer;
    font-size: 0.85rem;
    transition: var(--transition);
}

.btn-danger:hover {
    opacity: 0.8;
}

.btn-edit {
    background: var(--warning);
    color: white;
    border: none;
    border-radius: 6px;
    padding: 6px 12px;
    cursor: pointer;
    font-size: 0.85rem;
    transition: var(--transition);
}

.btn-edit:hover {
    opacity: 0.8;
}

section {
    margin-bottom: 30px;
}

h2 {
    margin-bottom: 15px;
    color: var(--text-primary);
    font-size: 1.5rem;
}

.add-friend {
    background: var(--bg-secondary);
    padding: 20px;
    border-radius: 12px;
    border: 1px solid var(--border);
}

.form-group {
    margin-bottom: 15px;
}

label {
    display: block;
    margin-bottom: 5px;
    font-weight: 600;
    color: var(--text-secondary);
}

input, select {
    width: 100%;
    padding: 10px;
    border: 1px solid var(--border);
    border-radius: 8px;
    background: var(--bg-primary);
    color: var(--text-primary);
    font-size: 1rem;
    transition: var(--transition);
}

input:focus, select:focus {
    outline: none;
    border-color: var(--accent-primary);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

#friend-form {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr 1fr;
    gap: 15px;
    align-items: end;
}

#friend-form button {
    grid-column: span 4;
}

.search-section {
    background: var(--bg-secondary);
    padding: 15px;
    border-radius: 12px;
    border: 1px solid var(--border);
}

.search-controls {
    display: grid;
    grid-template-columns: 2fr 1fr;
    gap: 15px;
}

.friends-list {
    background: var(--bg-secondary);
    border-radius: 12px;
    border: 1px solid var(--border);
    overflow: hidden;
}

.friends-list h2 {
    padding: 20px;
    margin: 0;
    background: var(--bg-tertiary);
}

.friend-item {
    padding: 15px 20px;
    border-bottom: 1px solid var(--border);
    display: grid;
    grid-template-columns: 1fr auto;
    gap: 15px;
    align-items: center;
    transition: var(--transition);
}

.friend-item:nth-child(odd) {
    background: var(--row-a);
}

.friend-item:nth-child(even) {
    background: var(--row-b);
}

.friend-item:last-child {
    border-bottom: none;
}

.friend-info h3 {
    margin-bottom: 5px;
    color: var(--text-primary);
    font-size: 1.1rem;
}

.friend-details {
    color: var(--text-secondary);
    font-size: 0.9rem;
    line-height: 1.4;
}

.friend-age {
    font-weight: 600;
    color: var(--accent-primary);
}

.monthly-age {
    font-weight: 500;
    color: var(--warning);
    font-size: 0.85rem;
}

.next-birthday {
    color: var(--success);
}

.friend-actions {
    display: flex;
    gap: 8px;
}

.no-data {
    padding: 40px 20px;
    text-align: center;
    color: var(--text-secondary);
    font-style: italic;
}

.hidden {
    display: none !important;
}

@media (max-width: 768px) {
    .container {
        padding: 15px;
    }
    
    header {
        flex-direction: column;
        gap: 15px;
        text-align: center;
    }
    
    #friend-form {
        grid-template-columns: 1fr;
    }
    
    #friend-form button {
        grid-column: span 1;
    }
    
    .search-controls {
        grid-template-columns: 1fr;
    }
    
    .friend-item {
        grid-template-columns: 1fr;
        gap: 10px;
    }
    
    .friend-actions {
        justify-content: center;
    }
}

@media (max-width: 480px) {
    h1 {
        font-size: 1.5rem;
    }
    
    .friend-item {
        padding: 12px 15px;
    }
    
    .friend-details {
        font-size: 0.85rem;
    }
}