Comment 6 for bug 2030963

> I think this bug should be reworded/simplified to only cover the window switcher and app switcher.

Fine by me. Edited.

> That in itself is a difficult design problem because the current highlight seems to be inherited from the shell theme. And we may want to keep it consistent with the highlighting used in the top panel

What highlighting in the top panel?

FWIW, if you have the Just Perfection extension (https://extensions.gnome.org/extension/3843/just-perfection/), you can have it override some theme stuff via ~/.local/share/gnome-shell/extensions/just-perfection-desktop@just-perfection/stylesheet.css. I have the following in there, and it works perfectly.

.just-perfection .switcher-list .item-box:selected
{
    background-color: #dd4814;
    color: #eeeeec;
}

> The orange frame in the workspace overview is not meant to be thin [because 4K]

The thickness is probably specified in pixels somewhere, which is a bug in itself. How many DPI a monitor has varies widely even between common native resolutions and sizes these days, and high-DPI displays are mainstream now. 32 " at 3840x2160 isn't even particularly high-DPI.

EDIT: found it. Here's a workaround for Just Perfection's stylesheet.css. Not pretty but it works:

.just-perfection .workspace-thumbnail-indicator
{
  border: 10px solid #dd4814;
  border-radius: 3px;
  padding: 0px;
}

> scaling factor 100% [...] is too low for 3840x2160. Please try changing Settings > Screen Display > Scale = 200%, or try enabling Fractional Scaling for values between 100% and 200%.

I've run 18.04 in this configuration (at 100 %) for years. It was fine; none of the UI elements were too small or otherwise too hard to see. I'd rather not waste my precious screen real estate by enabling scaling globally. There's literally no point in running a 4K screen at 200 %, might as well get a 1080p one.
That said, a little bit of scaling would be nice, so I tried the fractional option--but even 125 % is too much for my liking. (I do scale in applications, changing the scale factor dynamically as required.)