body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
}

header {
    background: #333;
    color: #fff;
    text-align: center;
    padding: 1em 0;
}
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

nav ul {
    list-style-type: none;
    padding: 0;
}

nav ul li {
    display: inline;
    margin: 0 10px;
}

nav ul li a {
    color: #fff;
    text-decoration: none;
}

section {
    padding: 2em;
}

.actividad {
    margin-bottom: 2em;
}

form label,
form input {
    display: block;
    margin-bottom: 1em;
}

form input {
    width: 100%;
    padding: 0.5em;
    border: 1px solid #ccc;
}

form input[type="submit"] {
    background: #333;
    color: #fff;
    border: none;
    cursor: pointer;
}