/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    line-height: 1.6;
    color: #333;
    background-color: #f8fafc;
}

/* Loading Screen */
.loading-screen {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    color: white;
    z-index: 9999;
}

.loading-spinner {
    width: 50px;
    height: 50px;
    border: 4px solid rgba(255, 255, 255, 0.3);
    border-top: 4px solid white;
    border-radius: 50%;
    animation: spin 1s linear infinite;
    margin-bottom: 20px;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* Main App */
.main-app {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header */
.header {
    background: white;
    border-bottom: 1px solid #e2e8f0;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 70px;
}

.logo h1 {
    font-size: 1.5rem;
    font-weight: 700;
    color: #4f46e5;
}

.nav {
    display: flex;
    gap: 10px;
}

.nav-btn {
    padding: 10px 20px;
    border: none;
    background: transparent;
    color: #64748b;
    font-weight: 500;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s ease;
}

.nav-btn:hover {
    background: #f1f5f9;
    color: #334155;
}

.nav-btn.active {
    background: #4f46e5;
    color: white;
}

.user-menu {
    display: flex;
    align-items: center;
    gap: 15px;
}

#user-name {
    font-weight: 500;
    color: #64748b;
}

/* Main Content */
.main-content {
    flex: 1;
    padding: 30px 0;
}

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

/* Sections */
.section {
    display: none;
}

.section.active {
    display: block;
}

.section h2 {
    font-size: 2rem;
    font-weight: 700;
    color: #1e293b;
    margin-bottom: 30px;
}

/* Dashboard Grid */
.dashboard-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 30px;
    margin-bottom: 30px;
}

/* Cards */
.card {
    background: white;
    border-radius: 12px;
    padding: 25px;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    border: 1px solid #e2e8f0;
}

.card h3 {
    font-size: 1.25rem;
    font-weight: 600;
    color: #1e293b;
    margin-bottom: 20px;
}

/* Stats Grid */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
}

.stat {
    text-align: center;
}

.stat-number {
    display: block;
    font-size: 2rem;
    font-weight: 700;
    color: #4f46e5;
    margin-bottom: 5px;
}

.stat-label {
    font-size: 0.875rem;
    color: #64748b;
    font-weight: 500;
}

/* Activity List */
.activity-list {
    max-height: 300px;
    overflow-y: auto;
}

.activity-item {
    padding: 15px 0;
    border-bottom: 1px solid #f1f5f9;
    display: flex;
    align-items: center;
    gap: 15px;
}

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

.activity-icon {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background: #e0e7ff;
    display: flex;
    align-items: center;
    justify-content: center;
    color: #4f46e5;
    font-size: 1.2rem;
}

.activity-content h4 {
    font-weight: 600;
    color: #1e293b;
    margin-bottom: 5px;
}

.activity-content p {
    font-size: 0.875rem;
    color: #64748b;
}

/* Assignment List */
.assignment-list {
    max-height: 300px;
    overflow-y: auto;
}

.assignment-item {
    padding: 15px 0;
    border-bottom: 1px solid #f1f5f9;
}

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

.assignment-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 10px;
}

.assignment-title {
    font-weight: 600;
    color: #1e293b;
}

.assignment-status {
    padding: 4px 12px;
    border-radius: 20px;
    font-size: 0.75rem;
    font-weight: 500;
}

.assignment-status.active {
    background: #dcfce7;
    color: #166534;
}

.assignment-status.completed {
    background: #dbeafe;
    color: #1e40af;
}

.assignment-description {
    font-size: 0.875rem;
    color: #64748b;
    margin-bottom: 10px;
}

.assignment-meta {
    display: flex;
    gap: 20px;
    font-size: 0.75rem;
    color: #94a3b8;
}

/* Action Buttons */
.action-buttons {
    display: flex;
    flex-direction: column;
    gap: 15px;
}

/* Buttons */
.btn {
    padding: 12px 24px;
    border: none;
    border-radius: 8px;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s ease;
    text-decoration: none;
    display: inline-block;
    text-align: center;
}

.btn-primary {
    background: #4f46e5;
    color: white;
}

.btn-primary:hover {
    background: #4338ca;
    transform: translateY(-1px);
}

.btn-secondary {
    background: #64748b;
    color: white;
}

.btn-secondary:hover {
    background: #475569;
    transform: translateY(-1px);
}

.btn-outline {
    background: transparent;
    color: #4f46e5;
    border: 2px solid #4f46e5;
}

.btn-outline:hover {
    background: #4f46e5;
    color: white;
    transform: translateY(-1px);
}

.btn-danger {
    background: #ef4444;
    color: white;
}

.btn-danger:hover {
    background: #dc2626;
    transform: translateY(-1px);
}

/* Modal */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 1000;
}

.modal-content {
    background: white;
    padding: 30px;
    border-radius: 12px;
    max-width: 500px;
    width: 90%;
    text-align: center;
}

.modal-content h3 {
    margin-bottom: 15px;
    color: #1e293b;
}

.modal-content p {
    margin-bottom: 20px;
    color: #64748b;
}

/* Forms */
.form-group {
    margin-bottom: 20px;
}

.form-label {
    display: block;
    margin-bottom: 8px;
    font-weight: 500;
    color: #374151;
}

.form-input {
    width: 100%;
    padding: 12px 16px;
    border: 1px solid #d1d5db;
    border-radius: 8px;
    font-size: 1rem;
    transition: border-color 0.2s ease;
}

.form-input:focus {
    outline: none;
    border-color: #4f46e5;
    box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
}

.form-textarea {
    min-height: 100px;
    resize: vertical;
}

/* Progress Bar */
.progress-bar {
    width: 100%;
    height: 8px;
    background: #e2e8f0;
    border-radius: 4px;
    overflow: hidden;
    margin: 10px 0;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, #4f46e5, #7c3aed);
    transition: width 0.3s ease;
}

/* Responsive Design */
@media (max-width: 768px) {
    .header-content {
        flex-direction: column;
        height: auto;
        padding: 15px 20px;
        gap: 15px;
    }

    .nav {
        order: 2;
    }

    .user-menu {
        order: 3;
    }

    .dashboard-grid {
        grid-template-columns: 1fr;
        gap: 20px;
    }

    .stats-grid {
        grid-template-columns: 1fr;
        gap: 15px;
    }

    .nav-btn {
        padding: 8px 16px;
        font-size: 0.875rem;
    }

    .section h2 {
        font-size: 1.5rem;
    }

    .card {
        padding: 20px;
    }
}

/* Dark Mode Support */
@media (prefers-color-scheme: dark) {
    body {
        background-color: #0f172a;
        color: #e2e8f0;
    }

    .header {
        background: #1e293b;
        border-bottom-color: #334155;
    }

    .card {
        background: #1e293b;
        border-color: #334155;
    }

    .section h2,
    .card h3 {
        color: #f1f5f9;
    }

    .nav-btn {
        color: #94a3b8;
    }

    .nav-btn:hover {
        background: #334155;
        color: #e2e8f0;
    }

    .form-input {
        background: #334155;
        border-color: #475569;
        color: #e2e8f0;
    }

    .form-input:focus {
        border-color: #6366f1;
    }
}

/* Animations */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.section.active {
    animation: fadeIn 0.3s ease;
}

/* Utility Classes */
.text-center {
    text-align: center;
}

.text-right {
    text-align: right;
}

.mb-20 {
    margin-bottom: 20px;
}

.mt-20 {
    margin-top: 20px;
}

.hidden {
    display: none;
}

.visible {
    display: block;
}