div.required, div.challenge, div.question, div.warning {
    margin-left: auto;
    margin-right: auto;
    margin-bottom: 1em;
    margin-top: 1em;
    width: 80%;
    background-color: #e0e0ff;
    padding-left: 1em;
    padding-right: 1em;
}

div.required .header {
    font-weight: bold;
}

div.challenge .header {
    font-style: italic;
}

div.question .header {
    font-weight: bold;
}

div.required {
    background-color: #e0e0ff;
    border: 1px solid #c0c0ff;
}

div.challenge {
    background-color: #ffe0e0;
    border: 1px solid #ffc0c0;
}

div.question {
    background-color: #e0e0ff;
    border: 1px solid #c0c0ff;
}

div.warning {
    background-color: #ffe0e0;
    border: 1px solid #ffc0c0;
}

kbd {
   color: #007700;
   font-family: monospace;
   font-weight: bold;
}