To apply, go to "Settings" > "Edit style sheet" > "Dictionary style sheet".

Example Qolibri CSS.css

* {
    font-family: 游明朝, "Yu Mincho", IPAMincho;
}
body {
    color: black;
    background-color: #fffaf0;
    margin: 0px;
}
h1 {
    background-color: #999999;
    color: #ffffff;
    font-weight: bold;
    font-size: x-large;
    margin: 0px;
    margin-bottom: 3px;
}
h2 {
    background-color: #e6e6e6;
    font-size: large;
    margin: 0px;
}
pre {
    background-color: #fffaf0;
    margin-left: 5px;
    margin-right: 0px;
    margin-top: 7px;
    margin-bottom: 7px;
    white-space: pre-wrap;
    text-indent: 15px;
    font-size: medium;
}
b {
    color: #393939;
}
em.err {
    color: #dd0000;
    font-weight: bold;
    font-style: italic;
}
span.sel {
    color: #551111;
}
span.img {
    font-size: small;
    font-style: italic;
}
img {
    vertical-align: super;
    font-size: small;
}
sup {
    color: #550000;
}
sub {
    color: #005500;
}
a {
    color: #0000ff;
}
a.cnd {
    color: #0000aa;
}