/* ===================================
   CSS CUSTOM PROPERTIES (VARIABLES)
   Advanced theming system - Project 1 Upskilled
   =================================== */

:root {
    /* Light Theme Colors - Purple (default) */
    --color-primary: #9333ea;
    --color-primary-dark: #7e22ce;
    --color-primary-light: #a855f7;
    
    --color-secondary: #f59e0b;
    --color-success: #10b981;
    --color-danger: #ef4444;
    --color-warning: #f59e0b;
    
    --color-bg-main: #faf5ff;
    --color-bg-card: #ffffff;
    --color-bg-hover: #f3e8ff;
    
    --color-text-primary: #0f172a;
    --color-text-secondary: #64748b;
    --color-text-tertiary: #94a3b8;
    
    --color-border: #e2e8f0;
    --color-border-dark: #cbd5e1;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 0.75rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    
    /* Typography */
    --font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-size-xs: 0.75rem;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;
    --font-size-3xl: 2rem;
    
    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    
    /* Transitions */
    --transition-fast: 150ms ease-in-out;
    --transition-base: 200ms ease-in-out;
    --transition-slow: 300ms ease-in-out;
}

/* Dark Theme - Purple */
[data-theme="dark"] {
    --color-bg-main: #1e1b4b;
    --color-bg-card: #312e81;
    --color-bg-hover: #3730a3;
    
    --color-text-primary: #f1f5f9;
    --color-text-secondary: #cbd5e1;
    --color-text-tertiary: #94a3b8;
    
    --color-border: #334155;
    --color-border-dark: #475569;
    
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4), 0 2px 4px -1px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4), 0 4px 6px -2px rgba(0, 0, 0, 0.3);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.5), 0 10px 10px -5px rgba(0, 0, 0, 0.4);
}

/* ===================================
   COLOR THEMES
   =================================== */

/* Blue Theme */
[data-color="blue"] {
    --color-primary: #3b82f6;
    --color-primary-dark: #2563eb;
    --color-primary-light: #60a5fa;
    
    --color-bg-main: #eff6ff;
    --color-bg-hover: #dbeafe;
}

[data-color="blue"][data-theme="dark"] {
    --color-bg-main: #1e3a5f;
    --color-bg-card: #1e40af;
    --color-bg-hover: #2563eb;
}

/* Green Theme */
[data-color="green"] {
    --color-primary: #10b981;
    --color-primary-dark: #059669;
    --color-primary-light: #34d399;
    
    --color-bg-main: #ecfdf5;
    --color-bg-hover: #d1fae5;
}

[data-color="green"][data-theme="dark"] {
    --color-bg-main: #064e3b;
    --color-bg-card: #065f46;
    --color-bg-hover: #047857;
}

/* Pink Theme */
[data-color="pink"] {
    --color-primary: #ec4899;
    --color-primary-dark: #db2777;
    --color-primary-light: #f472b6;
    
    --color-bg-main: #fdf2f8;
    --color-bg-hover: #fce7f3;
}

[data-color="pink"][data-theme="dark"] {
    --color-bg-main: #831843;
    --color-bg-card: #9f1239;
    --color-bg-hover: #be123c;
}

/* Orange Theme */
[data-color="orange"] {
    --color-primary: #f97316;
    --color-primary-dark: #ea580c;
    --color-primary-light: #fb923c;
    
    --color-bg-main: #fff7ed;
    --color-bg-hover: #ffedd5;
}

[data-color="orange"][data-theme="dark"] {
    --color-bg-main: #7c2d12;
    --color-bg-card: #9a3412;
    --color-bg-hover: #c2410c;
}

/* Red Theme */
[data-color="red"] {
    --color-primary: #ef4444;
    --color-primary-dark: #dc2626;
    --color-primary-light: #f87171;
    
    --color-bg-main: #fef2f2;
    --color-bg-hover: #fee2e2;
}

[data-color="red"][data-theme="dark"] {
    --color-bg-main: #7f1d1d;
    --color-bg-card: #991b1b;
    --color-bg-hover: #b91c1c;
}

/* ===================================
   RESET & BASE STYLES
   =================================== */

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

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    line-height: 1.6;
    color: var(--color-text-primary);
    background-color: var(--color-bg-main);
    transition: background-color var(--transition-base), color var(--transition-base);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* ===================================
   TYPOGRAPHY
   Advanced typography system - Project 1 Upskilled
   =================================== */

h1, h2, h3, h4, h5, h6 {
    font-weight: 600;
    line-height: 1.2;
    margin-bottom: var(--spacing-md);
}

h1 { font-size: var(--font-size-3xl); }
h2 { font-size: var(--font-size-2xl); }
h3 { font-size: var(--font-size-xl); }

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

/* ===================================
   LAYOUT - FLEXBOX & GRID
   Advanced layout system - Project 1 Upskilled
   =================================== */

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

.main {
    flex: 1;
    padding: var(--spacing-2xl) 0;
}

/* ===================================
   HEADER
   =================================== */

.header {
    background-color: var(--color-bg-card);
    border-bottom: 1px solid var(--color-border);
    padding: var(--spacing-lg) 0;
    box-shadow: var(--shadow-sm);
    position: sticky;
    top: 0;
    z-index: 100;
    transition: all var(--transition-base);
}

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

.logo {
    font-size: var(--font-size-xl);
    font-weight: 700;
    color: var(--color-primary);
    margin: 0;
}

.nav {
    display: flex;
    gap: var(--spacing-md);
}

/* ===================================
   BUTTONS
   Advanced button system with animations
   =================================== */

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-sm) var(--spacing-lg);
    font-size: var(--font-size-base);
    font-weight: 500;
    font-family: var(--font-family);
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-base);
    text-decoration: none;
    position: relative;
    overflow: hidden;
}

.btn::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.3);
    transform: translate(-50%, -50%);
    transition: width var(--transition-slow), height var(--transition-slow);
}

.btn:hover::before {
    width: 300px;
    height: 300px;
}

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

.btn-primary:hover {
    background-color: var(--color-primary-dark);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-secondary {
    background-color: var(--color-bg-hover);
    color: var(--color-text-primary);
    border: 1px solid var(--color-border);
}

.btn-secondary:hover {
    background-color: var(--color-border);
    transform: translateY(-2px);
}

.btn-block {
    width: 100%;
}

.btn:active {
    transform: translateY(0);
}

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

/* Theme Toggle */
.theme-icon {
    font-size: var(--font-size-lg);
}

/* ===================================
   UPLOAD SECTION
   Advanced drag & drop styling
   =================================== */

.upload-section {
    display: grid;
    grid-template-columns: 1fr auto 1fr;
    gap: var(--spacing-2xl);
    margin-bottom: var(--spacing-2xl);
    align-items: start;
}

.upload-card,
.add-assignment-card {
    background-color: var(--color-bg-card);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-md);
    transition: all var(--transition-base);
}

.upload-card:hover,
.add-assignment-card:hover {
    box-shadow: var(--shadow-lg);
    transform: translateY(-2px);
}

.upload-description {
    color: var(--color-text-secondary);
    font-size: var(--font-size-sm);
    margin-bottom: var(--spacing-lg);
}

.upload-area {
    border: 2px dashed var(--color-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-2xl);
    text-align: center;
    transition: all var(--transition-base);
    cursor: pointer;
}

.upload-area:hover {
    border-color: var(--color-primary);
    background-color: var(--color-bg-hover);
}

.upload-area.drag-over {
    border-color: var(--color-primary);
    background-color: var(--color-primary-light);
    background-color: rgba(99, 102, 241, 0.1);
    transform: scale(1.02);
}

.upload-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
}

.upload-text {
    font-weight: 500;
    color: var(--color-text-primary);
    margin-bottom: var(--spacing-xs);
}

.upload-subtext {
    font-size: var(--font-size-sm);
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-md);
}

.upload-status {
    margin-top: var(--spacing-md);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    font-size: var(--font-size-sm);
}

.upload-status.success {
    background-color: rgba(16, 185, 129, 0.1);
    color: var(--color-success);
    border: 1px solid var(--color-success);
}

.upload-status.error {
    background-color: rgba(239, 68, 68, 0.1);
    color: var(--color-danger);
    border: 1px solid var(--color-danger);
}

/* Divider */
.divider {
    display: flex;
    align-items: center;
    color: var(--color-text-tertiary);
    font-weight: 500;
    font-size: var(--font-size-sm);
}

/* ===================================
   FORMS
   Advanced form styling with validation
   =================================== */

.assignment-form {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.form-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-lg);
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

.form-group label {
    font-weight: 500;
    font-size: var(--font-size-sm);
    color: var(--color-text-secondary);
}

.form-group input,
.form-group select,
.form-group textarea {
    width: 100%;
    padding: var(--spacing-sm) var(--spacing-md);
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    color: var(--color-text-primary);
    background-color: var(--color-bg-main);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    transition: all var(--transition-base);
}

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

.form-group input:invalid:not(:placeholder-shown),
.form-group select:invalid:not(:placeholder-shown),
.form-group textarea:invalid:not(:placeholder-shown) {
    border-color: var(--color-danger);
}

.form-group textarea {
    resize: vertical;
    min-height: 80px;
}

/* ===================================
   STATISTICS SECTION
   CSS Grid layout - Project 1 Upskilled
   =================================== */

.stats-section {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-2xl);
}

.stat-card {
    background-color: var(--color-bg-card);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-md);
    display: flex;
    align-items: center;
    gap: var(--spacing-lg);
    transition: all var(--transition-base);
    border: 1px solid var(--color-border);
}

.stat-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-xl);
}

.stat-icon {
    font-size: 2.5rem;
    line-height: 1;
}

.stat-content {
    flex: 1;
}

.stat-label {
    font-size: var(--font-size-sm);
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-xs);
}

.stat-value {
    font-size: var(--font-size-3xl);
    font-weight: 700;
    color: var(--color-primary);
    margin: 0;
}

/* ===================================
   FILTER SECTION
   =================================== */

.filter-section {
    background-color: var(--color-bg-card);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-md);
    margin-bottom: var(--spacing-2xl);
}

.filter-controls {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-lg);
    align-items: flex-end;
}

.filter-group {
    flex: 1;
    min-width: 200px;
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

.filter-group label {
    font-weight: 500;
    font-size: var(--font-size-sm);
    color: var(--color-text-secondary);
}

.filter-select {
    padding: var(--spacing-sm) var(--spacing-md);
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    color: var(--color-text-primary);
    background-color: var(--color-bg-main);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    transition: all var(--transition-base);
    cursor: pointer;
}

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

/* ===================================
   ASSIGNMENTS LIST
   =================================== */

.assignments-section {
    margin-bottom: var(--spacing-2xl);
}

.section-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: var(--spacing-xl);
    gap: var(--spacing-lg);
    flex-wrap: wrap;
}

.section-title {
    margin: 0;
    color: var(--color-text-primary);
}

.course-legend {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-md);
    align-items: center;
}

.legend-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-xs) var(--spacing-sm);
    background-color: var(--color-bg-card);
    border-radius: var(--radius-md);
    font-size: var(--font-size-sm);
    box-shadow: var(--shadow-sm);
}

.legend-color {
    width: 16px;
    height: 16px;
    border-radius: 50%;
    display: inline-block;
    box-shadow: 0 0 0 2px rgba(255, 255, 255, 0.3);
}

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

.assignments-list {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

/* Empty State */
.empty-state {
    background-color: var(--color-bg-card);
    border-radius: var(--radius-lg);
    padding: var(--spacing-2xl);
    text-align: center;
    box-shadow: var(--shadow-md);
}

.empty-icon {
    font-size: 4rem;
    margin-bottom: var(--spacing-lg);
    opacity: 0.5;
}

.empty-state h3 {
    color: var(--color-text-primary);
    margin-bottom: var(--spacing-sm);
}

.empty-state p {
    color: var(--color-text-secondary);
    margin: 0;
}

/* Assignment Card */
.assignment-card {
    background-color: var(--color-bg-card);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-md);
    border-left: 6px solid var(--color-border);
    transition: all var(--transition-base);
    animation: slideIn 0.3s ease-out;
    position: relative;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.assignment-card:hover {
    box-shadow: var(--shadow-lg);
    transform: translateX(4px);
}

.assignment-card.completed {
    opacity: 0.7;
}

.assignment-card.completed::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: var(--color-success);
    opacity: 0.05;
    border-radius: var(--radius-lg);
    pointer-events: none;
}

.assignment-card.overdue::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: var(--color-danger);
    opacity: 0.03;
    border-radius: var(--radius-lg);
    pointer-events: none;
}

.assignment-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: var(--spacing-md);
}

.assignment-title {
    font-size: var(--font-size-lg);
    font-weight: 600;
    color: var(--color-text-primary);
    margin: 0;
}

.assignment-card.completed .assignment-title {
    text-decoration: line-through;
    opacity: 0.6;
}

.assignment-actions {
    display: flex;
    gap: var(--spacing-sm);
}

.icon-btn {
    background: none;
    border: none;
    font-size: var(--font-size-lg);
    cursor: pointer;
    padding: var(--spacing-xs);
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.icon-btn:hover {
    background-color: var(--color-bg-hover);
    transform: scale(1.1);
}

.assignment-meta {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-md);
}

.meta-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    font-size: var(--font-size-sm);
    color: var(--color-text-secondary);
}

.course-indicator {
    font-weight: 600;
    color: var(--color-text-primary);
}

.course-color-dot {
    width: 12px;
    height: 12px;
    border-radius: 50%;
    display: inline-block;
    box-shadow: 0 0 0 2px rgba(255, 255, 255, 0.3);
    flex-shrink: 0;
}

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

.badge-priority-high {
    background-color: rgba(239, 68, 68, 0.1);
    color: var(--color-danger);
}

.badge-priority-medium {
    background-color: rgba(245, 158, 11, 0.1);
    color: var(--color-warning);
}

.badge-priority-low {
    background-color: rgba(16, 185, 129, 0.1);
    color: var(--color-success);
}

.badge-status {
    background-color: rgba(99, 102, 241, 0.1);
    color: var(--color-primary);
}

.badge-overdue {
    background-color: rgba(239, 68, 68, 0.1);
    color: var(--color-danger);
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0%, 100% {
        opacity: 1;
    }
    50% {
        opacity: 0.6;
    }
}

.assignment-notes {
    font-size: var(--font-size-sm);
    color: var(--color-text-secondary);
    line-height: 1.6;
    margin-top: var(--spacing-md);
    padding-top: var(--spacing-md);
    border-top: 1px solid var(--color-border);
}

/* ===================================
   MODAL
   =================================== */

.modal {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    backdrop-filter: blur(4px);
    z-index: 1000;
    align-items: center;
    justify-content: center;
    animation: fadeIn 0.2s ease-out;
}

.modal.active {
    display: flex;
}

@keyframes fadeIn {
    from {
        opacity: 0;
    }
    to {
        opacity: 1;
    }
}

.modal-content {
    background-color: var(--color-bg-card);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    max-width: 600px;
    width: 90%;
    max-height: 90vh;
    overflow-y: auto;
    box-shadow: var(--shadow-xl);
    animation: slideUp 0.3s ease-out;
}

@keyframes slideUp {
    from {
        transform: translateY(50px);
        opacity: 0;
    }
    to {
        transform: translateY(0);
        opacity: 1;
    }
}

.modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-xl);
}

.modal-close {
    background: none;
    border: none;
    font-size: 2rem;
    cursor: pointer;
    color: var(--color-text-secondary);
    transition: all var(--transition-fast);
    line-height: 1;
    padding: 0;
    width: 32px;
    height: 32px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: var(--radius-sm);
}

.modal-close:hover {
    background-color: var(--color-bg-hover);
    color: var(--color-text-primary);
    transform: rotate(90deg);
}

.modal-actions {
    display: flex;
    gap: var(--spacing-md);
    justify-content: flex-end;
    margin-top: var(--spacing-xl);
}

/* ===================================
   TOAST NOTIFICATIONS
   =================================== */

.toast {
    position: fixed;
    bottom: var(--spacing-xl);
    right: var(--spacing-xl);
    background-color: var(--color-bg-card);
    color: var(--color-text-primary);
    padding: var(--spacing-md) var(--spacing-xl);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-xl);
    border-left: 4px solid var(--color-primary);
    z-index: 2000;
    transform: translateX(400px);
    transition: transform var(--transition-base);
    max-width: 400px;
}

.toast.show {
    transform: translateX(0);
}

.toast.success {
    border-left-color: var(--color-success);
}

.toast.error {
    border-left-color: var(--color-danger);
}

.toast.warning {
    border-left-color: var(--color-warning);
}

/* ===================================
   FOOTER
   =================================== */

.footer {
    background-color: var(--color-bg-card);
    border-top: 1px solid var(--color-border);
    padding: var(--spacing-xl) 0;
    text-align: center;
    margin-top: auto;
}

.footer p {
    color: var(--color-text-secondary);
    font-size: var(--font-size-sm);
    margin: 0;
}

/* ===================================
   RESPONSIVE DESIGN
   Multiple breakpoints - Project 1 Upskilled
   =================================== */

/* Tablet Landscape (1024px) */
@media (max-width: 1024px) {
    .upload-section {
        grid-template-columns: 1fr;
    }
    
    .divider {
        justify-content: center;
    }
    
    .stats-section {
        grid-template-columns: repeat(2, 1fr);
    }
}

/* Tablet Portrait (768px) */
@media (max-width: 768px) {
    :root {
        --font-size-3xl: 1.75rem;
        --font-size-2xl: 1.375rem;
        --spacing-2xl: 2rem;
    }
    
    .container {
        padding: 0 var(--spacing-md);
    }
    
    .header {
        padding: var(--spacing-md) 0;
    }
    
    .logo {
        font-size: var(--font-size-lg);
    }
    
    .form-row {
        grid-template-columns: 1fr;
    }
    
    .filter-controls {
        flex-direction: column;
    }
    
    .filter-group {
        width: 100%;
    }
    
    .stats-section {
        grid-template-columns: 1fr;
    }
}

/* Mobile (480px) */
@media (max-width: 480px) {
    :root {
        --spacing-xl: 1.5rem;
        --spacing-lg: 1rem;
    }
    
    .upload-card,
    .add-assignment-card {
        padding: var(--spacing-lg);
    }
    
    .upload-area {
        padding: var(--spacing-xl);
    }
    
    .assignment-card {
        padding: var(--spacing-lg);
    }
    
    .assignment-header {
        flex-direction: column;
        gap: var(--spacing-md);
    }
    
    .assignment-actions {
        width: 100%;
        justify-content: flex-start;
    }
    
    .modal-content {
        width: 95%;
        padding: var(--spacing-lg);
    }
    
    .toast {
        right: var(--spacing-md);
        left: var(--spacing-md);
        max-width: none;
    }
}

/* ===================================
   ACCESSIBILITY
   =================================== */

/* Focus visible for keyboard navigation */
*:focus-visible {
    outline: 2px solid var(--color-primary);
    outline-offset: 2px;
}

/* Reduced motion for accessibility */
@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

/* High contrast mode support */
@media (prefers-contrast: high) {
    :root {
        --color-border: #000000;
        --color-text-secondary: #000000;
    }
    
    [data-theme="dark"] {
        --color-border: #ffffff;
        --color-text-secondary: #ffffff;
    }
}

/* Screen reader only content */
.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border-width: 0;
}

/* ===================================
   COURSE MANAGEMENT
   =================================== */

.welcome-content,
.manage-courses-content {
    padding: var(--spacing-md) 0;
}

.welcome-content p {
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-xl);
}

.course-input-group {
    display: flex;
    gap: var(--spacing-sm);
}

.course-input-group input {
    flex: 1;
    padding: var(--spacing-sm) var(--spacing-md);
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    color: var(--color-text-primary);
    background-color: var(--color-bg-main);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    transition: all var(--transition-base);
}

.course-input-group input:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(147, 51, 234, 0.1);
}

.courses-list,
.manage-courses-list {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
    margin-top: var(--spacing-md);
    max-height: 300px;
    overflow-y: auto;
}

.course-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-md);
    background-color: var(--color-bg-main);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    transition: all var(--transition-base);
}

.course-item:hover {
    background-color: var(--color-bg-hover);
}

.course-name {
    font-weight: 500;
    color: var(--color-text-primary);
}

.remove-course {
    background: none;
    border: none;
    color: var(--color-danger);
    cursor: pointer;
    font-size: var(--font-size-lg);
    padding: var(--spacing-xs);
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.remove-course:hover {
    background-color: rgba(239, 68, 68, 0.1);
    transform: scale(1.1);
}

.manage-courses-list {
    min-height: 150px;
}

.manage-courses-list:empty::before {
    content: 'No courses added yet. Add your first course above!';
    display: block;
    padding: var(--spacing-xl);
    text-align: center;
    color: var(--color-text-tertiary);
    font-style: italic;
}

/* ===================================
   COLOR PICKER
   =================================== */

.color-picker-content {
    padding: var(--spacing-md) 0;
}

.color-picker-content p {
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-xl);
}

.color-options {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: var(--spacing-lg);
}

.color-option {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-lg);
    background-color: var(--color-bg-main);
    border: 2px solid var(--color-border);
    border-radius: var(--radius-lg);
    cursor: pointer;
    transition: all var(--transition-base);
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    font-weight: 500;
}

.color-option:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
    border-color: var(--color-primary);
}

.color-option.active {
    border-color: var(--color-primary);
    border-width: 3px;
    background-color: var(--color-bg-hover);
}

.color-preview {
    width: 60px;
    height: 60px;
    border-radius: 50%;
    box-shadow: var(--shadow-md);
    transition: transform var(--transition-base);
}

.color-option:hover .color-preview {
    transform: scale(1.1);
}

/* Color Previews */
.purple-preview {
    background: linear-gradient(135deg, #9333ea 0%, #c084fc 100%);
}

.blue-preview {
    background: linear-gradient(135deg, #3b82f6 0%, #60a5fa 100%);
}

.green-preview {
    background: linear-gradient(135deg, #10b981 0%, #34d399 100%);
}

.pink-preview {
    background: linear-gradient(135deg, #ec4899 0%, #f472b6 100%);
}

.orange-preview {
    background: linear-gradient(135deg, #f97316 0%, #fb923c 100%);
}

.red-preview {
    background: linear-gradient(135deg, #ef4444 0%, #f87171 100%);
}

@media (max-width: 768px) {
    .color-options {
        grid-template-columns: repeat(2, 1fr);
    }
}