:root {
    /* Primary Color Palette */
    --primary: #6366F1;
    --primary-dark: #4F46E5;
    --primary-light: #818CF8;
    
   /* Semantic Colors */
    --success: #22C55E;
    --warning: #F59E0B;
    --error: #EF4444;
    
    /* Priority Colors */
    --priority-high: #EF4444;
    --priority-medium: #F59E0B;
    --priority-low: #22C55E;
    
    /* Category Colors */
    --category-work: #3B82F6;
    --category-personal: #8B5CF6;
    --category-health: #10B981;
    --category-finance: #F59E0B;
    --category-study: #EC4899;
    
    /* Light Mode */
    --bg-primary: #FAFAFA;
    --bg-secondary: #FFFFFF;
    --text-primary: #0F0F0F;
    --text-secondary: #6B7280;
    --border-color: #E5E7EB;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.1);
    
    /* Spacing */
    --spacing-xs: 4px;
    --spacing-sm: 8px;
    --spacing-md: 16px;
    --spacing-lg: 24px;
    --spacing-xl: 32px;
    --spacing-2xl: 48px;
    
    /* Border Radius */
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 24px;
    --radius-full: 9999px;
    
    /* Typography */
    --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    --font-size-xs: 12px;
    --font-size-sm: 14px;
    --font-size-base: 16px;
    --font-size-lg: 18px;
    --font-size-xl: 20px;
    --font-size-2xl: 24px;
    --font-size-3xl: 30px;
    --font-size-4xl: 36px;
    
    /* Transitions */
    --transition: all 0.2s ease-in-out;
    --transition-slow: all 0.3s ease-in-out;
}

/* Dark Mode */
[data-theme="dark"] {
    --bg-primary: #0F0F0F;
    --bg-secondary: #1A1A1A;
    --text-primary: #FFFFFF;
    --text-secondary: #9CA3AF;
    --border-color: #2D2D2D;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.5);
}

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

html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--bg-primary);
    transition: background-color 0.3s ease, color 0.3s ease;
}

/* Container */
.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

.container-narrow {
    max-width: 800px;
}

.container-wide {
    max-width: 1400px;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

h1 { font-size: var(--font-size-4xl); }
h2 { font-size: var(--font-size-3xl); }
h3 { font-size: var(--font-size-2xl); }
h4 { font-size: var(--font-size-xl); }
h5 { font-size: var(--font-size-lg); }
h6 { font-size: var(--font-size-base); }

p {
    margin-bottom: var(--spacing-md);
    color: var(--text-secondary);
}

a {
    color: var(--primary);
    text-decoration: none;
    transition: var(--transition);
}

a:hover {
    color: var(--primary-dark);
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    padding: 12px 24px;
    font-size: var(--font-size-base);
    font-weight: 500;
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: var(--transition);
    text-decoration: none;
    min-height: 48px;
}

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

.btn-primary:hover {
    background: var(--primary-dark);
    transform: translateY(-1px);
    box-shadow: var(--shadow-lg);
}

.btn-secondary {
    background: transparent;
    color: var(--primary);
    border: 2px solid var(--primary);
}

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

.btn-success {
    background: var(--success);
    color: white;
}

.btn-success:hover {
    filter: brightness(1.1);
}

.btn-danger {
    background: var(--error);
    color: white;
}

.btn-danger:hover {
    filter: brightness(1.1);
}

.btn-sm {
    padding: 8px 16px;
    font-size: var(--font-size-sm);
    min-height: 36px;
}

.btn-lg {
    padding: 16px 32px;
    font-size: var(--font-size-lg);
    min-height: 56px;
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none !important;
}

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

.card:hover {
    box-shadow: var(--shadow-lg);
}

.card-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: var(--spacing-md);
    padding-bottom: var(--spacing-md);
    border-bottom: 1px solid var(--border-color);
}

.card-title {
    font-size: var(--font-size-xl);
    font-weight: 600;
    margin: 0;
}

.card-body {
    padding: 0;
}

/* Forms */
.form-group {
    margin-bottom: var(--spacing-md);
}

.form-label {
    display: block;
    font-size: var(--font-size-sm);
    font-weight: 500;
    margin-bottom: var(--spacing-sm);
    color: var(--text-primary);
}

.form-input,
.form-select,
.form-textarea {
    width: 100%;
    padding: 12px 16px;
    font-size: var(--font-size-base);
    font-family: var(--font-family);
    color: var(--text-primary);
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    transition: var(--transition);
    min-height: 48px;
}

.form-input:focus,
.form-select:focus,
.form-textarea:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

.form-textarea {
    min-height: 120px;
    resize: vertical;
}

.form-checkbox {
    width: 20px;
    height: 20px;
    cursor: pointer;
    accent-color: var(--primary);
}

/* Grid */
.grid {
    display: grid;
    gap: var(--spacing-md);
}

.grid-2 {
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
}

.grid-3 {
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
}

.grid-4 {
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
}

/* Flex Utilities */
.flex {
    display: flex;
}

.flex-col {
    flex-direction: column;
}

.items-center {
    align-items: center;
}

.justify-between {
    justify-content: space-between;
}

.justify-center {
    justify-content: center;
}

.gap-sm { gap: var(--spacing-sm); }
.gap-md { gap: var(--spacing-md); }
.gap-lg { gap: var(--spacing-lg); }

/* Spacing Utilities */
.mt-sm { margin-top: var(--spacing-sm); }
.mt-md { margin-top: var(--spacing-md); }
.mt-lg { margin-top: var(--spacing-lg); }
.mt-xl { margin-top: var(--spacing-xl); }

.mb-sm { margin-bottom: var(--spacing-sm); }
.mb-md { margin-bottom: var(--spacing-md); }
.mb-lg { margin-bottom: var(--spacing-lg); }
.mb-xl { margin-bottom: var(--spacing-xl); }

.p-sm { padding: var(--spacing-sm); }
.p-md { padding: var(--spacing-md); }
.p-lg { padding: var(--spacing-lg); }
.p-xl { padding: var(--spacing-xl); }

/* Text Utilities */
.text-center { text-align: center; }
.text-right { text-align: right; }
.text-sm { font-size: var(--font-size-sm); }
.text-lg { font-size: var(--font-size-lg); }
.text-xl { font-size: var(--font-size-xl); }
.text-primary { color: var(--text-primary) !important; }
.text-secondary { color: var(--text-secondary) !important; }
.text-success { color: var(--success) !important; }
.text-warning { color: var(--warning) !important; }
.text-error { color: var(--error) !important; }
.font-bold { font-weight: 700; }
.font-semibold { font-weight: 600; }
.font-medium { font-weight: 500; }

/* Badges */
.badge {
    display: inline-flex;
    align-items: center;
    padding: 4px 12px;
    font-size: var(--font-size-xs);
    font-weight: 500;
    border-radius: var(--radius-full);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.badge-primary { background: var(--primary); color: white; }
.badge-success { background: var(--success); color: white; }
.badge-warning { background: var(--warning); color: white; }
.badge-error { background: var(--error); color: white; }
.badge-high { background: var(--priority-high); color: white; }
.badge-medium { background: var(--priority-medium); color: white; }
.badge-low { background: var(--priority-low); color: white; }

/* Loading Spinner */
.spinner {
    width: 40px;
    height: 40px;
    border: 4px solid var(--border-color);
    border-top-color: var(--primary);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Toast Notifications */
.toast {
    position: fixed;
    bottom: var(--spacing-lg);
    right: var(--spacing-lg);
    min-width: 300px;
    padding: var(--spacing-md);
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    transform: translateY(100px);
    opacity: 0;
    transition: var(--transition-slow);
    z-index: 1000;
}

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

.toast-success { border-left: 4px solid var(--success); }
.toast-warning { border-left: 4px solid var(--warning); }
.toast-error { border-left: 4px solid var(--error); }

/* Modal */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 999;
    opacity: 0;
    pointer-events: none;
    transition: var(--transition);
}

.modal-overlay.show {
    opacity: 1;
    pointer-events: all;
}

.modal {
    background: var(--bg-secondary);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    max-width: 600px;
    width: 90%;
    max-height: 90vh;
    overflow-y: auto;
    box-shadow: var(--shadow-lg);
    transform: scale(0.9);
    transition: var(--transition);
}

.modal-overlay.show .modal {
    transform: scale(1);
}

/* Responsive */
@media (max-width: 768px) {
    :root {
        --font-size-4xl: 28px;
        --font-size-3xl: 24px;
        --font-size-2xl: 20px;
    }
    
    .grid-2,
    .grid-3,
    .grid-4 {
        grid-template-columns: 1fr;
    }
    
    .container {
        padding: 0 var(--spacing-sm);
    }
}