/* Define color variables for easy theme management */
:root {
    --primary-dark: #004d40;
    --primary-main: #00796b;
    --primary-light: #e0f2f1;
    --text-light: #fff;
    --text-dark: #333;
    --background-light: #f4f4f4;
    --border-color: #ccc;
}

body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    background-color: var(--background-light);
    color: var(--text-dark);
    line-height: 1.6;
    scroll-behavior: smooth; /* Adds smooth scrolling for anchor links */
}

header {
    background-color: var(--primary-dark);
    color: var(--text-light);
    text-align: center;
    padding: 1rem 0;
}

header h1 {
    margin: 0;
}

nav {
    background-color: var(--primary-main);
    padding: 0.5rem 0;
    text-align: center;
}

nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    justify-content: center;
}

nav li a {
    color: var(--text-light);
    text-decoration: none;
    padding: 0.5rem 1rem;
    display: block;
}

nav li a:hover {
    background-color: var(--primary-dark);
}

nav li a.nav-active {
    background-color: var(--primary-dark);
    font-weight: bold;
    border-bottom: 3px solid var(--primary-light);
}

main {
    padding: 2rem;
    max-width: 900px;
    margin: auto;
}

section {
    background-color: #fff;
    padding: 2rem;
    margin-bottom: 2rem;
    border-radius: 8px;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

.lesson-container {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
    justify-content: center;
}

.lesson {
    background-color: var(--primary-light);
    padding: 1.5rem;
    border-radius: 8px;
    flex-basis: calc(33.333% - 1rem); /* 3 lessons per row on larger screens */
    box-sizing: border-box;
}

.btn {
    display: inline-block;
    background-color: var(--primary-main);
    color: var(--text-light);
    padding: 0.5rem 1rem;
    text-decoration: none;
    border-radius: 4px;
    margin-top: 1rem;
}

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

/* Styles for lesson content pages */
.lesson-navigation {
    margin-top: 2rem;
    border-top: 1px solid var(--border-color);
    padding-top: 1.5rem;
    display: flex;
    justify-content: space-between;
    flex-wrap: wrap;
    gap: 1rem;
}

.btn.btn-disabled {
    background-color: #aaa;
    cursor: not-allowed;
}

#lesson-content ul {
    list-style-position: inside;
}

.official-guidance {
    background-color: #fafafa;
    border: 1px solid #eee;
    border-left: 5px solid var(--primary-main);
    padding: 1rem 1.5rem;
    margin-top: 2rem;
    border-radius: 0 8px 8px 0;
}

.official-guidance h4 {
    margin-top: 0;
    color: var(--primary-dark);
}

.toc-list ul {
    padding-left: 2rem;
}

.resource-chapter {
    padding: 2rem 0;
    border-bottom: 1px solid var(--border-color);
}

.resource-title {
    padding-bottom: 1rem;
    border-bottom: 2px solid var(--primary-dark);
}

.search-container {
    margin: 1.5rem 0;
}

#resource-search {
    width: 100%;
    padding: 0.75rem;
}

.office-hours-content {
    text-align: center;
    padding: 1rem;
}

.bio-content {
    display: flex;
    align-items: center;
    gap: 1.5rem;
}

.bio-content img {
    border-radius: 50%;
    border: 3px solid var(--primary-main);
}

form label, form input, form textarea {
    display: block;
    width: 100%;
    margin-bottom: 1rem;
}

form input, form textarea {
    padding: 0.5rem;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    box-sizing: border-box; /* Ensures padding doesn't affect width */
}

form button {
    background-color: var(--primary-main);
    color: var(--text-light);
    padding: 0.75rem 1.5rem;
    border: none;
    cursor: pointer;
    border-radius: 4px;
    width: auto;
}

form button:hover {
    background-color: var(--primary-dark);
}

#form-status {
    margin-top: 1rem;
    color: var(--primary-dark);
    font-weight: bold;
}

footer {
    text-align: center;
    padding: 1rem 0;
    background-color: var(--text-dark);
    color: var(--text-light);
}

/* --- Responsive Design --- */

/* For tablets and smaller devices */
@media (max-width: 768px) {
    .lesson {
        /* 2 lessons per row */
        flex-basis: calc(50% - 1rem);
    }

    .bio-content {
        flex-direction: column;
        text-align: center;
    }

    nav ul {
        flex-direction: column;
    }
}

/* For mobile phones */
@media (max-width: 480px) {
    .lesson {
        /* 1 lesson per row */
        flex-basis: 100%;
    }
}