div.lemma {
    border-style: solid;
    border-width: 1px;
    padding: 5px;
    margin-bottom: 10px;
    margin-top: 10px;
}

div.proof {
    margin-bottom: 40px;
    margin-top: 10px;
}

div.proof:after {
    content: '';
    float: right;
    width: 14px;
    height: 14px;
    border-style: solid;
    border-width: 1px;
}

div.bsp {
    margin-bottom: 10px;
    margin-top: 10px;
}