:root {
    --primary-color: #007bff;
    --secondary-color: #6c757d;
    --background-color: #f8f9fa;
    --text-color: #333;
    --header-bg: #212529;
    --header-text: #ffffff;
    --card-bg: #ffffff;
    --code-bg: #282c34;
    --code-text: #abb2bf;
    --border-color: #dee2e6;
    --font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

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

body {
    font-family: var(--font-family);
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--background-color);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 15px;
}

header {
    background-color: var(--header-bg);
    color: var(--header-text);
    padding: 1rem 0;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

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

header h1 {
    font-size: 1.8rem;
}

nav a {
    color: var(--header-text);
    text-decoration: none;
    margin-left: 1rem;
    padding: 0.5rem 0.8rem;
    border-radius: 4px;
    transition: background-color 0.3s;
}

nav a:hover, nav a.active {
    background-color: rgba(255, 255, 255, 0.1);
}

main {
    flex-grow: 1;
    padding: 2rem 0;
}

.view {
    display: none;
    animation: fadeIn 0.5s ease-in-out;
}

.view.active {
    display: block;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Hero Section */
.hero {
    text-align: center;
    padding: 4rem 0;
    background-color: var(--card-bg);
    border-radius: 8px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
}

.hero h2 {
    color: var(--primary-color);
    margin-bottom: 1rem;
    font-size: 2.5rem;
}

#start-learning-btn {
    background-color: var(--primary-color);
    color: white;
    border: none;
    padding: 0.75rem 1.5rem;
    font-size: 1.1rem;
    border-radius: 5px;
    cursor: pointer;
    margin-top: 1.5rem;
    transition: background-color 0.3s;
}

#start-learning-btn:hover {
    background-color: #0056b3;
}

/* Lesson Structure */

.lesson-list {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 20px;
}

.lesson-card {
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 20px;
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.05);
    transition: transform 0.2s;
    cursor: pointer;
}

.lesson-card:hover {
    transform: translateY(-5px);
    border-color: var(--primary-color);
}

.lesson-card h3 {
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

/* Lesson Detail View */
#lesson-detail-view {
    padding: 20px;
    background-color: var(--card-bg);
    border-radius: 8px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
}

#lesson-detail-view h2 {
    border-bottom: 3px solid var(--primary-color);
    padding-bottom: 10px;
    margin-bottom: 20px;
}

.content-section h3 {
    margin-top: 1.5rem;
    color: #495057;
}

p {
    margin-bottom: 1rem;
}

/* Code Snippets */
pre {
    background-color: var(--code-bg);
    color: var(--code-text);
    padding: 1rem;
    border-radius: 5px;
    overflow-x: auto;
    margin: 1rem 0;
    font-family: 'Consolas', 'Monaco', monospace;
    font-size: 0.9rem;
}

code {
    font-family: 'Consolas', 'Monaco', monospace;
    background-color: #e9ecef;
    padding: 2px 4px;
    border-radius: 3px;
    color: #c90000; /* Inline code highlight */
}

pre code {
    background-color: transparent;
    padding: 0;
    color: var(--code-text);
}

/* Tables for data structure explanation */
.responsive-table-container {
    overflow-x: auto;
    margin: 1rem 0;
}

table {
    width: 100%;
    border-collapse: collapse;
    margin: 1rem 0;
    background-color: var(--card-bg);
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.05);
}

table th, table td {
    padding: 12px 15px;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
}

table th {
    background-color: #e9e9e9;
    color: var(--text-color);
    font-weight: 600;
}

/* Back button style */
.back-btn {
    background: none;
    border: 1px solid var(--secondary-color);
    color: var(--secondary-color);
    padding: 5px 10px;
    border-radius: 4px;
    cursor: pointer;
    margin-bottom: 20px;
    transition: background-color 0.2s, color 0.2s;
}

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


/* Footer */
footer {
    background-color: var(--header-bg);
    color: var(--header-text);
    text-align: center;
    padding: 1rem 0;
    margin-top: auto;
}

/* Responsiveness */
@media (max-width: 600px) {
    header .container {
        flex-direction: column;
        text-align: center;
    }
    
    header h1 {
        margin-bottom: 10px;
    }

    nav a {
        margin: 0 0.5rem;
        padding: 0.5rem;
    }
    
    .hero {
        padding: 2rem 1rem;
    }
}