"Only groups" toggle button in the popup's search filters does not have an "activated" (toggled) look, and the "Extended search" checkbox is misleading

[nekohayo]

To Reproduce
Steps to reproduce the behavior:

1. Press F8 to open the extension's popup menu
2. Type any search term
3. Notice the "Only groups" button on the right of the search bar, click it, and notice that it doesn't look any different

Expected behavior
The state of that button should look different when it is activated than when it is not; this would be particularly useful because that state is remembered across searches/instances of the popup widget, so it is currently visually impossible to know if it was left activated or not.

My suggestion is to either style it like a true togglebutton, or to use a "checkbox with label" widget (where clicking the label also toggles the checkbox, and the visual relationship is clear).

On that note, as you can see in the screenshots below, there currently is a checkbox-without-label widget on the left of that button already, but that one is unrelated and does something completely different ("Extended search", whatever that is?). It would need a label, too.

Screenshots

Current appearance, with Firefox in dark mode...

...when the button is not activated (and we see the "Extended search" unlabelled checkbox, which adds to the confusion):

...when the button is activated:

In both situations, it is really not visually obvious what is going on there.

Desktop:

• OS and version: Fedora 39 (Linux)
• Firefox version: 121
• Simple Tab Groups version: 5.2