Template:Did you know/styles.css

/* Did you know header styling */
.dyk-header {
    border-width: 1px;
    border-style: solid;
    margin-top: 3px;
    margin-bottom: 0.5em;
    padding: 0.2em 0.4em;
    font-size: 120%;
    font-weight: bold;
    font-family: inherit;
    background: #cedff2;
    border-color: #a3b0bf;
}

/* Dark mode support for Did you know header */
html.skin-theme-clientpref-night .dyk-header {
    background-color: #082849;
    border-color: #a3b0bf;
    color: #e8e6e3;
}

/* OS dark mode support for Did you know header */
@media screen and (prefers-color-scheme: dark) {
    html.skin-theme-clientpref-os .dyk-header {
        background-color: #082849;
        border-color: #a3b0bf;
        color: #e8e6e3;
    }
}