Editing Module:Sidebar/styles.css

/* {{pp-template}} */
/* TODO: Invert width design to be "mobile first" */
.sidebar {
	/* TODO: Ask if we should have max-width 22em instead */
	width: 22em;
	/* @noflip */
	float: right;
	/* @noflip */
	clear: right;
	/* @noflip */
	margin: 0.5em 0 1em 1em;
	background: var(--background-color-neutral-subtle, #f8f9fa);
	border: 1px solid #aaa;
	padding: 0.2em;
	text-align: center;
	line-height: 1.4em;
	font-size: 88%;
	border-collapse: collapse;
	/* Timeless has display: none on .nomobile at mobile resolutions, so we
	 * unhide it with display: table and let precedence and proximity win.
	 */
	display: table; 
}

/* Unfortunately, so does Minerva desktop, except Minerva drops an
 * !important on the declaration. So we have to be mean for Minerva users.
 * Mobile removes the element entirely with `wgMFRemovableClasses` in 
 * https://github.com/wikimedia/operations-mediawiki-config/blob/master/
 wmf-config/InitialiseSettings.php#L16992
 * which is why displaying it categorically with display: table works.
 * We don't really want to expose the generic user in the wild on mobile to have
 * to deal with sidebars. (Maybe the ones with collapsible lists, so that
 * might be an improvement. That is blocked on [[:phab:T111565]].)
 */
body.skin-minerva .sidebar {
	display: table !important;
	/* also, minerva is way too aggressive about other stylings on tables.
	 * TODO remove when this template gets moved to a div. plans on talk page.
	 * We always float right on Minerva because that's a lot of extra CSS
	 * otherwise. */
    float: right !important;
    margin: 0.5em 0 1em 1em !important;
}

.sidebar-subgroup {
	width: 100%;
	margin: 0;
	border-spacing: 0;
}

.sidebar-left {
	/* @noflip */
	float: left;
	/* @noflip */
	clear: left;
	/* @noflip */
	margin: 0.5em 1em 1em 0;
}

.sidebar-none {
	float: none;
	clear: both;
	/* @noflip */
	margin: 0.5em 1em 1em 0;
}

.sidebar-outer-title {
	padding: 0 0.4em 0.2em;
	font-size: 125%;
	line-height: 1.2em;
	font-weight: bold;
}

.sidebar-top-image {
	padding: 0.4em;
}

.sidebar-top-caption,
.sidebar-pretitle-with-top-image,
.sidebar-caption {
	padding: 0.2em 0.4em 0;
	line-height: 1.2em;
}

.sidebar-pretitle {
	padding: 0.4em 0.4em 0;
	line-height: 1.2em;
}

.sidebar-title,
.sidebar-title-with-pretitle {
	padding: 0.2em 0.8em;
	font-size: 145%;
	line-height: 1.2em;
}

.sidebar-title-with-pretitle {
	padding: 0.1em 0.4em;
}

.sidebar-image {
	padding: 0.2em 0.4em 0.4em;
}

.sidebar-heading {
	padding: 0.1em 0.4em;
}

.sidebar-content {
	padding: 0 0.5em 0.4em;
}

.sidebar-content-with-subgroup {
	padding: 0.1em 0.4em 0.2em;
}

.sidebar-above,
.sidebar-below {
	padding: 0.3em 0.8em;
	font-weight: bold;
}

.sidebar-collapse .sidebar-above,
.sidebar-collapse .sidebar-below {
	border-top: 1px solid #aaa;
	border-bottom: 1px solid #aaa;
}

.sidebar-navbar {
	text-align: right;
	font-size: 115%;
	padding: 0 0.4em 0.4em;
}

.sidebar-list-title {
	padding: 0 0.4em;
	text-align: left;
	font-weight: bold;
	line-height: 1.6em;
	font-size: 105%;
}

/* centered text with mw-collapsible headers is finicky */
.sidebar-list-title-c {
	padding: 0 0.4em;
	text-align: center;
	margin: 0 3.3em;
}

@media (max-width: 720px) {
	/* users have wide latitude to set arbitrary width and margin :(
	   "Super-specific" selector to prevent overriding this appearance by
	   lower level sidebars too */
	body.mediawiki .sidebar {
		width: 100% !important;
		clear: both;
		float: none !important; /* Remove when we div based; Minerva is dumb */
		margin-left: 0 !important;
		margin-right: 0 !important;
	}
	/* TODO: We might consider making all links wrap at small resolutions and then
	 * only introduce nowrap at higher resolutions. Do when we invert the media
	 * query.
	 */
}


/* Disable backgrounds via style attribute in night mode Eg.https://phabricator.wikimedia.org/F55243859 / https://en.wikipedia.org/w/index.php?title=Laissez-faire */
html.skin-theme-clientpref-night .sidebar-list-title,
html.skin-theme-clientpref-night .sidebar-title-with-pretitle {
    background: transparent !important;
}
@media (prefers-color-scheme: dark) {
    /* automatic mode */
    html.skin-theme-clientpref-os .sidebar:not( .notheme ) .sidebar-list-title,
    html.skin-theme-clientpref-os .sidebar:not( .notheme ) .sidebar-title-with-pretitle {
       background: transparent !important;
    }
}