Workaround to add border to the dock does not work when custom colour and/or dynamic opacity is selected

[n3thshan]

Description

The quick workaround to add the border as suggested by @micheleg is as follows:

#dashtodockContainer .dash-background {
     border: 1px solid grey !important;
}

However the issue is that the border disappears as soon i try to customize the dash colour and/or if i set opacity to dynamic. The workaround only works with the toggle off for dash colour AND/OR when opacity is selected as "Default" or "Fixed"

Steps to reproduce

1. Add the workaround above to the stylesheet.css file
2. Go to dock settings>Appearance
3. Toggle on customize the dash colour AND/OR under customize opacity, select "Dynamic"

Observed result

Border does not appear

Expected result

Border should be persistent across any setting regardless

[vanvugt]

Since the feature doesn't exist yet, let's group this with #1883.

[vanvugt]

Duplicate of #1883