Editing Template:Helpbox/styles.css

/* {{pp|small=y}} */
.help-box {
	background: #f5faff;
	line-height: 1.6em;
}

.help-box .sidebar-title {
	background: #cee0f2;
	font-size: 130%;
	padding-left: 0.4em;
	padding-right: 0.4em; /* gap before first heading/content */
	margin-bottom: 6px;
}

.help-box .sidebar-heading {
	background: #cee0f2;
	padding: 0.1em 0.7em 0.15em;
}

.help-box .sidebar-content,
/* conservatively target subgroups since we're working with a metatemplate */
.help-box .sidebar-content-with-subgroup {
	padding-top: 0.15em;
}

@media all and (min-width: 720px) {
	.help-box {
		width: auto;
		max-width: 22em;
	}
}

html.skin-theme-clientpref-night .help-box {
	background: #0d1a27;
}
html.skin-theme-clientpref-night .help-box .sidebar-title,
html.skin-theme-clientpref-night .help-box .sidebar-heading {
	background: #082849;
}
@media screen and (prefers-color-scheme: dark) {
	html.skin-theme-clientpref-os .help-box {
		background-color: #0d1a27;
	}
	html.skin-theme-clientpref-os .help-box .sidebar-title,
	html.skin-theme-clientpref-os .help-box .sidebar-heading {
		background: #082849;
	}
}