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

/* Typography - System fonts for scalability and performance */
body {
    font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    line-height: 1.6;
    color: #333;
    background-color: #fff;
}

/* Layout */
body {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header */
header {
    margin-bottom: 3rem;
    text-align: center;
    border-bottom: 1px solid #e5e5e5;
    padding-bottom: 2rem;
}

header h1 {
    font-size: 2.5rem;
    font-weight: 700;
    color: #1a365d;
    margin-bottom: 0.5rem;
}

/* Main content */
main {
    flex: 1;
}

.intro {
    margin-bottom: 3rem;
    font-size: 1.1rem;
    text-align: left;
}

.intro p {
    margin-bottom: 1rem;
    max-width: 800px;
    margin-left: auto;
    margin-right: auto;
}

/* Section styling */
.course-materials h2 {
    font-size: 2rem;
    font-weight: 600;
    color: #2d3748;
    margin-bottom: 2rem;
    text-align: center;
}

.course-category {
    margin-bottom: 2.5rem;
    background: #f7fafc;
    border-radius: 8px;
    padding: 2rem;
    border-left: 4px solid #3182ce;
}

.course-category h3 {
    font-size: 1.5rem;
    font-weight: 600;
    color: #2d3748;
    margin-bottom: 1.5rem;
}

/* List styling */
ul {
    list-style: none;
}

ul li {
    margin-bottom: 1rem;
    padding-left: 1.5rem;
    position: relative;
}

ul li::before {
    content: "→";
    position: absolute;
    left: 0;
    color: #3182ce;
    font-weight: bold;
}

/* Link styling */
a {
    color: #3182ce;
    text-decoration: none;
    font-weight: 500;
    transition: color 0.2s ease-in-out;
}

a:hover {
    color: #2c5282;
    text-decoration: underline;
}

a:focus {
    outline: 2px solid #3182ce;
    outline-offset: 2px;
}

/* Note styling */
.note {
    color: #718096;
    font-style: italic;
    font-size: 0.9rem;
}

/* Footer */
footer {
    margin-top: 4rem;
    padding-top: 2rem;
    border-top: 1px solid #e5e5e5;
    text-align: center;
    color: #718096;
}

/* Responsive design */
@media (max-width: 768px) {
    body {
        padding: 1rem;
    }
    
    header h1 {
        font-size: 2rem;
    }
    
    .course-materials h2 {
        font-size: 1.75rem;
    }
    
    .course-category h3 {
        font-size: 1.25rem;
    }
    
    .course-category {
        padding: 1.5rem;
    }
}

@media (max-width: 480px) {
    header h1 {
        font-size: 1.75rem;
    }
    
    .intro {
        font-size: 1rem;
    }
    
    .course-category {
        padding: 1rem;
    }
}

/* Print styles */
@media print {
    body {
        color: #000;
        background: #fff;
        font-size: 12pt;
        line-height: 1.4;
    }
    
    a {
        color: #000;
        text-decoration: underline;
    }
    
    .course-category {
        background: #fff;
        border: 1px solid #ccc;
    }
}