h1, h2, h3, h4 {
    font-size: 24px;
    -webkit-text-stroke: 1px black; 
}

.gioithieu {
    background-color: #F3FDE8;
    padding: 15px;
}

.lienhe {
    background-image: url("image9.jpg");
    background-repeat: repeat;
    text-align: center;
    padding: 20px;
}

table, th, td {
    border: 1px solid black;
    border-collapse: collapse;
    padding: 5px;
}

nav {
    background-color: #d4f2f4;
    padding: 10px;
    text-align: center;
}

nav a {
    color: #0b0848;
    margin: 0 10px;
    text-decoration: none;
    font-weight: bold;
}

footer {
    background-color: #d4f2f4;
    text-align: center;
    padding: 10px;
}

footer p {
    color: #0b0848;
}

/* --------Bài tập 3------------- */
/* A */ 
.gioithieu img:hover {
    transform: scale(1.1);
    box-shadow: 0 0 15px rgba(0, 0, 0, 0.4);
}

.error {
    color: red;
    font-size: 14px;
    margin: 2px 0 10px;
}

input[type="submit"] {
    background-color: #fff;
    border: 1px solid #ccc;
    padding: 8px 15px;
    border-radius: 5px;
    font-weight: bold;
    transition: background-color 0.3s ease, color 0.3s ease;
}

input[type="submit"]:hover {
    background-color: #D8B4F8;
    color: white;
    cursor: pointer;
}

/* B */ 
.completed {
    background-color: #c6f5c6;
    text-decoration: line-through;
}

/* C */ 
.hovered {
    transform: scale(1.05);
    border: 3px solid #9F70FD;
    box-shadow: 0 0 15px rgba(159, 112, 253, 0.5);
}

#backToTop {
    position: fixed;
    bottom: 20px;
    right: 25px;
    display: none;
    background-color: #D8B4F8;
    color: white;
    border: none;
    border-radius: 8px;
    padding: 10px 15px;
    font-weight: bold;
    cursor: pointer;
    box-shadow: 0 0 10px rgba(0,0,0,0.3);
    transition: transform 0.3s ease, background-color 0.3s ease;
}

#backToTop:hover {
    transform: scale(1.1);
    background-color: #b07bfa;
}