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

:root {
    --primary-color: #2c3e50;
    --secondary-color: #3498db;
    --accent-color: #27ae60;
    --bg-color: #f8f9fa;
    --card-bg: #ffffff;
    --text-primary: #2c3e50;
    --text-secondary: #7f8c8d;
    --border-color: #e1e8ed;
    --shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
    --shadow-hover: 0 4px 16px rgba(0, 0, 0, 0.15);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
    width: 100%;
}

/* Header */
header {
    background: var(--primary-color);
    color: white;
    padding: 2rem 0;
    text-align: center;
    box-shadow: var(--shadow);
}

header h1 {
    font-size: 2rem;
    margin-bottom: 0.5rem;
    font-weight: 600;
}

.subtitle {
    font-size: 1rem;
    opacity: 0.9;
    font-weight: 300;
}

/* Main Content */
main {
    flex: 1;
    padding: 2rem 0;
}

/* Search Bar */
.search-container {
    position: relative;
    margin-bottom: 2rem;
}

#searchInput {
    width: 100%;
    padding: 1rem 3rem 1rem 1rem;
    font-size: 1rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    background: var(--card-bg);
    transition: border-color 0.3s;
}

#searchInput:focus {
    outline: none;
    border-color: var(--secondary-color);
}

#clearSearch {
    position: absolute;
    right: 1rem;
    top: 50%;
    transform: translateY(-50%);
    background: none;
    border: none;
    font-size: 1.5rem;
    color: var(--text-secondary);
    cursor: pointer;
    display: none;
    padding: 0;
    width: 24px;
    height: 24px;
    line-height: 1;
}

#clearSearch:hover {
    color: var(--text-primary);
}

/* Semester Tabs */
.semester-tabs {
    display: flex;
    gap: 1rem;
    margin-bottom: 2rem;
    border-bottom: 2px solid var(--border-color);
}

.semester-tab {
    padding: 1rem 2rem;
    font-size: 1rem;
    border: none;
    background: none;
    color: var(--text-secondary);
    cursor: pointer;
    border-bottom: 3px solid transparent;
    transition: all 0.3s;
    font-weight: 500;
}

.semester-tab:hover {
    color: var(--text-primary);
}

.semester-tab.active {
    color: var(--secondary-color);
    border-bottom-color: var(--secondary-color);
}

/* Semester Content */
.semester-content {
    display: none;
}

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

/* Lessons Grid */
.lessons-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 1.5rem;
}

.lesson-card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 1.5rem;
    cursor: pointer;
    transition: all 0.3s;
    position: relative;
}

.lesson-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-hover);
    border-color: var(--secondary-color);
}

.lesson-number {
    font-size: 0.875rem;
    color: var(--text-secondary);
    font-weight: 500;
    margin-bottom: 0.5rem;
}

.lesson-title {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
}

.lesson-description {
    font-size: 0.875rem;
    color: var(--text-secondary);
    line-height: 1.5;
}

.lesson-progress {
    position: absolute;
    top: 1rem;
    right: 1rem;
    width: 24px;
    height: 24px;
    background: var(--accent-color);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-size: 0.875rem;
}

.lesson-card:not(.completed) .lesson-progress {
    display: none;
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: 4rem 2rem;
    color: var(--text-secondary);
    font-size: 1.125rem;
}

/* Modal */
.modal {
    display: none;
    position: fixed;
    z-index: 1000;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    backdrop-filter: blur(4px);
    animation: fadeIn 0.3s;
}

.modal.active {
    display: flex;
    align-items: center;
    justify-content: center;
}

.modal-content {
    background: var(--card-bg);
    border-radius: 12px;
    max-width: 600px;
    width: 90%;
    max-height: 90vh;
    overflow-y: auto;
    animation: slideUp 0.3s;
}

.modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1.5rem;
    border-bottom: 1px solid var(--border-color);
}

.modal-header h2 {
    font-size: 1.5rem;
    font-weight: 600;
}

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

.close-btn:hover {
    color: var(--text-primary);
}

.modal-body {
    padding: 1.5rem;
}

/* Progress Indicator */
.progress-indicator {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem;
    background: var(--bg-color);
    border-radius: 8px;
    margin-bottom: 1.5rem;
}

#progressText {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.progress-indicator.completed #progressText {
    color: var(--accent-color);
    font-weight: 500;
}

/* Materials List */
.materials-list {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
    margin-bottom: 1.5rem;
}

.material-item {
    display: flex;
    align-items: center;
    padding: 1rem;
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    text-decoration: none;
    color: var(--text-primary);
    transition: all 0.3s;
}

.material-item:hover {
    background: var(--card-bg);
    border-color: var(--secondary-color);
    transform: translateX(4px);
}

.material-icon {
    font-size: 1.5rem;
    margin-right: 1rem;
}

.material-name {
    flex: 1;
    font-weight: 500;
}

.material-type {
    font-size: 0.75rem;
    color: var(--text-secondary);
    background: var(--card-bg);
    padding: 0.25rem 0.75rem;
    border-radius: 12px;
    border: 1px solid var(--border-color);
}

/* Buttons */
.btn-primary,
.btn-secondary {
    padding: 0.75rem 1.5rem;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s;
}

.btn-primary {
    background: var(--secondary-color);
    color: white;
    width: 100%;
}

.btn-primary:hover {
    background: #2980b9;
    transform: translateY(-2px);
}

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

.btn-secondary:hover {
    background: var(--card-bg);
    border-color: var(--accent-color);
}

.progress-indicator.completed .btn-secondary {
    background: var(--accent-color);
    color: white;
    border-color: var(--accent-color);
}

/* Footer */
footer {
    background: var(--primary-color);
    color: white;
    text-align: center;
    padding: 1.5rem 0;
    margin-top: 2rem;
}

footer p {
    margin: 0.25rem 0;
    font-size: 0.875rem;
}

footer a {
    color: white;
    text-decoration: none;
    opacity: 0.9;
}

footer a:hover {
    opacity: 1;
    text-decoration: underline;
}

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

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

/* Responsive Design */
@media (max-width: 768px) {
    header h1 {
        font-size: 1.5rem;
    }

    .lessons-grid {
        grid-template-columns: 1fr;
    }

    .semester-tab {
        padding: 0.75rem 1rem;
        font-size: 0.875rem;
    }

    .modal-content {
        width: 95%;
    }

    .progress-indicator {
        flex-direction: column;
        gap: 1rem;
        align-items: flex-start;
    }

    .btn-secondary {
        width: 100%;
    }
}