body {
    font-family: Arial, sans-serif;
    display: flex;
    flex-direction: column;
    margin: 0;
    padding: 0;
}
h1 {
    text-align: center;
    background: #2c3e50;
    color: white;
    margin: 0;
    padding: 1em 0;
}
.container {
    display: flex;
    height: calc(100vh - 80px);
}
.sidebar {
    width: 25%;
    background: #ecf0f1;
    padding: 1em;
    overflow-y: auto;
}
.viewer {
    width: 75%;
    padding: 1em;
}
iframe {
    width: 100%;
    height: 100%;
    border: 1px solid #ccc;
}
ul {
    list-style-type: none;
    padding-left: 1em;
}
a {
    text-decoration: none;
    color: #2980b9;
}
a:hover {
    text-decoration: underline;
}
.collapsible {
    cursor: pointer;
    user-select: none;
    display: inline-block;
    margin-bottom: 5px;
}
.content {
    display: none;
    padding-left: 15px;
}
.collapsible.active {
    font-weight: bold;
}