Hi @Orfur, thanks for taking the time to report this and welcome to Wikimedia Phabricator! For future reference, please use the bug report form (linked from the top of the task creation page) to create a bug report, and fill in all the sections in the template. Thanks.
Unfortunately this Wikimedia Phabricator task lacks some information. If you have time and can still reproduce the situation: Please add a more complete description to this task, including your exact MediaWiki version and the exact extension version which are shown on Special:Version. Thanks!

In T405009#11195007, @Aklapper wrote:

Hi @Orfur, thanks for taking the time to report this and welcome to Wikimedia Phabricator! For future reference, please use the bug report form (linked from the top of the task creation page) to create a bug report, and fill in all the sections in the template. Thanks.
Unfortunately this Wikimedia Phabricator task lacks some information. If you have time and can still reproduce the situation: Please add a more complete description to this task, including your exact MediaWiki version and the exact extension version which are shown on Special:Version. Thanks!

I added them, but I don't think they're necessary for this situation. I couldn't figure out how to add the relevant template.

Changing the relevant section of ApprovedRevs.css as follows will solve the problem.

.approved-revision {
  background-color: var(--background-color-success-subtle, #d5fdf4) !important;
}

li.approved-revision {
  border-color: var(--border-color-success, #00af89) !important;
}

tr.approved-revision td {
  border-top: solid var(--border-color-success, #00af89) 2px !important;
  border-bottom: solid var(--border-color-success, #00af89) 2px !important;
}

tr.approved-revision td:first-child {
  border-left: solid var(--border-color-success, #00af89) 2px !important;
}

tr.approved-revision td:last-child {
  border-right: solid var(--border-color-success, #00af89) 2px !important;
}

@Orfur - thank you for looking into this. I agree that switching to variables is the way to go - it's what I've been doing with my other extensions also. I will try to get this done soon.

Change #1189884 had a related patch set uploaded (by Yaron Koren; author: Yaron Koren):

[mediawiki/extensions/ApprovedRevs@master] Change some hardcoded colors to variables, for dark mode compat

https://gerrit.wikimedia.org/r/1189884

Change #1189884 merged by jenkins-bot:

[mediawiki/extensions/ApprovedRevs@master] Change some hardcoded colors to variables, for dark mode compat

https://gerrit.wikimedia.org/r/1189884