body {
    font-family: Arial, sans-serif;
}

nav {
    background-color: #DDDDFF;
    color: white;
    padding: 10px;
    text-align: center;
}

nav a {
    display: inline-block;
    color: #3344AA;
    text-decoration: none;
    padding: 10px 20px;
    transition: background-color 0.3s;
}

nav button {
    color: white;
    background-color: #3344AA;
    border: none;
    padding: 10px 20px;
    margin: 0 5px;
    cursor: pointer;
}

nav button:hover {
    background-color: #3344AA;
}

code {
    font-family: 'Courier New', Courier, monospace;
}

.sidebar {
    position: fixed;
    left: 0;
    top: 0;
    width: 12%;
    height: 100%;
    background-color: #DDDDFF90;
    overflow: auto;
    font-size: 20px;
}

.section {
    margin-bottom: 20px;
}

.toggle {
    background-color: #3344AA50;
    width: 100%;
    padding: 10px;
    border: none;
    cursor: pointer;
    font-size: 20px;
}

.chapters {
    background-color: #DDDDFF90;
    display: none;
    padding: 0;
    font-size: 20px;
}

.chapter {
    background-color: #DDDDFF90;
    padding: 10px;
    cursor: pointer;
}

.chapter h3 {
    margin: 0;
}

.chapters ul {
    list-style-type: none;
    padding: 0;
}

.chapters li {
    padding: 10px;
    cursor: pointer;
}

.chapters li:hover {
    background-color: #ddd;
}

.content {
    margin-left: 12%;
    padding: 20px;
    font-size: 20px;
}

.chapter-content {
    display: none;
}

.attention {
    background-color: #fff0f090;
    border-left: 5px solid #ff4d4d;
    padding: 10px;
    margin: 10px 0;
}
.extend {
    background-color: #f4f4f490;
    border-left: 5px solid #f4f4f4;
    padding: 10px;
    margin: 10px 0;
}

/* .background {
    background: url('https://bestdori.com/assets/cn/characters/resourceset/res021069_rip/card_after_training.png') no-repeat center center fixed;
  } */