body {
    width: 90%;
    max-width: 1000px;
    margin: auto;
}

h1 {
    color: blue;
    align: center;
}

h2 {
    color: #006eff;
    text-indent: 15px;
}

h3 {
    color: green;
    text-indent: 30px;
}

pre {
    background-color: #fbfaf9;
    color: #333;
    border: 1px solid lightgrey;
    /*margin-left: 30px;*/
    padding: 15px;
}

p {
    /*text-indent: 30px;*/
    text-align: justify;
}

table {
    border-collapse: collapse;
    margin-bottom: 50px;
    min-width: 50%;
}

th {
    border: 1px solid gray;
    padding: 0.3em 0.5em 0.3em 0.3em;
    background-color: #eee;
    text-align: left;
}

td {
    border: 1px solid #ccc;
    padding: 0.3em 0.5em 0.3em 0.3em;
    vertical-align: top;
}

.ejercicio {
    color: green;
    font-size: 20px;
    background-color: lightgoldenrodyellow;
}

.contenidos {
    border: 1px solid blue;
    background-color: lightseagreen;
}

a:link {
    text-decoration: none;
}

a {
    color: green;
}

a:hover {
    text-decoration: underline;
}

a.urlexterna {
    background: url(data:image/png;base64,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) no-repeat 0 center;
    padding: 0 0 0 18px;
    color: blue;
}

a.extension_7z {
    background: url(data:image/png;base64,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) no-repeat 0 center;
    padding: 0 0 0 18px;
    color: blue;
}