/* CSS Variables */
:root {
    --primary-color: #4a90e2;
    --secondary-color: #5cb85c;
    --danger-color: #d9534f;
    --background-color: #f5f5f5;
    --card-background: #ffffff;
    --text-color: #333333;
    --border-color: #dddddd;
    --spacing-small: 8px;
    --spacing-medium: 16px;
    --spacing-large: 24px;
    --border-radius: 8px;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    background-color: var(--background-color);
    color: var(--text-color);
    line-height: 1.6;
}

/* Utility Classes */
.hidden {
    display: none !important;
}

.btn {
    padding: var(--spacing-small) var(--spacing-medium);
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: 1rem;
    transition: background-color 0.2s;
}

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

.btn-primary:hover {
    background-color: #357abd;
}

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

.btn-secondary:hover {
    background-color: #4cae4c;
}

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

.btn-danger:hover {
    background-color: #c9302c;
}

.card {
    background: var(--card-background);
    border-radius: var(--border-radius);
    padding: var(--spacing-large);
    margin-bottom: var(--spacing-large);
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.form-group {
    margin-bottom: var(--spacing-medium);
}

.form-group label {
    display: block;
    margin-bottom: var(--spacing-small);
    font-weight: 600;
}

.form-group input[type="text"],
.form-group input[type="password"],
.form-group input[type="number"],
.form-group textarea,
.form-group select {
    width: 100%;
    padding: var(--spacing-small);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    font-size: 1rem;
}

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

.checkbox-group label {
    display: flex;
    align-items: center;
    font-weight: normal;
}

.checkbox-group input[type="checkbox"] {
    margin-right: var(--spacing-small);
    width: auto;
}

/* View Containers */
.view {
    max-width: 1200px;
    margin: 0 auto;
    padding: var(--spacing-large);
}

/* Login View */
.login-container {
    max-width: 500px;
    margin: 100px auto;
    text-align: center;
}

.login-container h1 {
    margin-bottom: var(--spacing-large);
    color: var(--primary-color);
}

.login-sections {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-large);
}

.login-section {
    background: var(--card-background);
    padding: var(--spacing-large);
    border-radius: var(--border-radius);
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.login-section h2 {
    margin-bottom: var(--spacing-medium);
    color: var(--text-color);
}

.login-section input,
.login-section select {
    width: 100%;
    margin-bottom: var(--spacing-medium);
}

/* Admin View */
.admin-header,
.student-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-large);
    padding-bottom: var(--spacing-medium);
    border-bottom: 2px solid var(--border-color);
}

.admin-tabs {
    display: flex;
    gap: var(--spacing-medium);
    margin-bottom: var(--spacing-large);
}

.tab-btn {
    padding: var(--spacing-small) var(--spacing-medium);
    background: var(--border-color);
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
}

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

.tab-content {
    display: none;
}

.tab-content.active {
    display: block;
}

/* List Container */
.list-container {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-medium);
}

.list-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-medium);
    background: var(--background-color);
    border-radius: var(--border-radius);
}

.list-item-info h3 {
    margin-bottom: var(--spacing-small);
}

.list-item-info p {
    color: #666;
    font-size: 0.9rem;
}

/* Student View */
.lessons-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: var(--spacing-large);
}

.lesson-card {
    background: var(--card-background);
    padding: var(--spacing-large);
    border-radius: var(--border-radius);
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    cursor: pointer;
    transition: transform 0.2s;
}

.lesson-card:hover {
    transform: translateY(-4px);
}

.lesson-card h3 {
    margin-bottom: var(--spacing-small);
    color: var(--primary-color);
}

/* Lesson Detail */
.lesson-detail-card {
    max-width: 800px;
    margin: 0 auto;
}

.material-section,
.submission-section,
.grading-section {
    margin-top: var(--spacing-large);
    padding-top: var(--spacing-medium);
    border-top: 1px solid var(--border-color);
}

.material-section a {
    color: var(--primary-color);
    text-decoration: none;
}

.material-section a:hover {
    text-decoration: underline;
}

/* List Item Actions */
.list-item-actions {
    display: flex;
    gap: var(--spacing-small);
}

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

.modal-content {
    background: var(--card-background);
    padding: var(--spacing-large);
    border-radius: var(--border-radius);
    width: 90%;
    max-width: 500px;
    max-height: 90vh;
    overflow-y: auto;
    position: relative;
}

.modal-content h2 {
    margin-bottom: var(--spacing-medium);
    color: var(--primary-color);
}

.close-modal {
    position: absolute;
    top: var(--spacing-medium);
    right: var(--spacing-medium);
    font-size: 1.5rem;
    cursor: pointer;
    color: #666;
    background: none;
    border: none;
    padding: var(--spacing-small);
}

.close-modal:hover {
    color: var(--danger-color);
}

/* Submission List */
.submission-list {
    margin-bottom: var(--spacing-medium);
}

.submission-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-small);
    background: var(--background-color);
    border-radius: var(--border-radius);
    margin-bottom: var(--spacing-small);
}

.submission-item .score {
    font-weight: 600;
    color: var(--primary-color);
}

/* File Input */
input[type="file"] {
    padding: var(--spacing-small);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    width: 100%;
    cursor: pointer;
}

input[type="file"]::file-selector-button {
    padding: var(--spacing-small) var(--spacing-medium);
    background: var(--primary-color);
    color: white;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    margin-right: var(--spacing-small);
}

input[type="file"]::file-selector-button:hover {
    background: #357abd;
}

/* Responsive */
@media (max-width: 768px) {
    .admin-tabs {
        flex-direction: column;
    }
    
    .lessons-grid {
        grid-template-columns: 1fr;
    }
    
    .login-sections {
        flex-direction: column;
    }
    
    .list-item {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-small);
    }
    
    .list-item-actions {
        width: 100%;
        justify-content: flex-end;
    }
    
    .submission-item {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-small);
    }
}