/* Element selector */
body {
    font-family: Arial, sans-serif;
    margin: 40px;
    max-width: 800px;
}

h1 {
    color: navy;
}

h2 {
    color: #333;
    border-bottom: 1px solid #ccc;
}

a {
    color: navy;
}

#header-section {
    background-color: #f0f0f0;
    padding: 15px;
    border: 1px solid #ccc;
}

/* Class selector */
.description {
    color: #555;
    line-height: 1.6;
}

/* ID selector */
#btree-img {
    border: 1px solid #aaa;
    padding: 8px;
    margin-top: 10px;
}