body {
    font-family: Arial;
    margin: 0;
}

header,
nav,
section,
article,
aside,
footer {
    padding: 15px;
    margin: 10px;
    border: 1px solid #ccc;
}

nav a {
    margin: 5px;
    cursor: pointer;
    color: blue;
}

.caja {
    width: 200px;
    height: 100px;
    background: lightblue;
    margin: 10px;
}

.resaltado {
    background: yellow;
    color: black;
    font-weight: bold;
}

button {
    margin: 5px;
}

footer {
    background: #f1f1f1;
    text-align: center;
}