#gioi-thieu {
    background-color: #F3FDE8;
}
#giao-luu {
    background: url("anh2.jpg") repeat;
    text-align: center;
}
h1, h2, h3, h4 {
    font-size: 24px;
    -webkit-text-stroke: 1px black;
}
table, th, td {
    border: 1px solid black;
    border-collapse: collapse;
    padding: 5px;
}
nav, footer {
    background-color: #d4f2f4;
    color: #0b0848;
    text-align: center;
    padding: 10px;
}
#backToTop {
    display: none;
    position: fixed;
    bottom: 20px;
    right: 30px;
    padding: 10px 15px;
    background-color: #6c63ff;
    color: white;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    font-size: 16px;
}

#backToTop:hover {
    background-color: #5149d1;
}