Fixed #34627 -- Highlighted active row in admin UI when forced-colors mode is enabled.

[nmenezes0]

Fixes https://code.djangoproject.com/ticket/34627

This PR adds highlighting on selected models in the admin sidebar and changelist when using "forced-colors".

For selected models in the admin and changelist:

This is what you currently see with forced-colors:

This PR changes this to:

[nessita]

Thank you for this work! For those (like me) that had no idea how to test this in Firefox, I followed https://hacks.mozilla.org/2020/07/adding-prefers-contrast-to-firefox/ and set the colors to "Override the colors specified by the page with your selections above" -> "Always".

I used the default colors from Firefox, and this is how it looks:

I was wondering if the row highlight could be... ligther? different? so the text on the highlighted row is easier to read. Right now the bold violet on top of dark cyan (?) seems challenging.

EDIT: After some googling (I'm not CSS expert), it seems that the SelectedItem value for background-color would use whatever my browser has configured so my suggestion does not make sense in that context.

[nessita]

Approving since this is working as expected, will wait a few days before merging to ensure other reviewers get the chance to review as well.

[thibaudcolas]

Thank you for giving this a go @nmenezes0. Result is looking great.

[nmenezes0]

Thank you for giving this a go @nmenezes0. Result is looking great.

Thanks for all your help!

[felixxm]

@nmenezes0 Thanks 👍