Scrollbar corners are not being colored according to the theme

[rinart73]

Current Behavior

Scrollbar corners appear when an element has both vertical and horizontal scrollbars.
Currently Skeleton doesn't apply any styles to them, so their apperance depends on a browser.
On the screenshot below - scrollbar corner in the bottom right is white because my OS and Chrome mode is light, even though website mode is dark.

Expected Behavior

Expected to have scrollbar corner be styled according to the theme settings and mode (light/dark).

Steps To Reproduce

1. Use any component/tag.
2. Ensure that it has both scrollbars. Example:

<div class="overflow-auto w-20 h-32">
  Lorem ipsum dolor sit amet, consectetur adipiscing elit.
  Aenean sed sagittis nibh, vel sollicitudin justo.
  Etiam dapibus ultricies felis, sit amet pellentesque justo sollicitudin sed.
  Suspendisse potenti.
</div>

Link to Reproduction / Stackblitz

https://stackblitz.com/edit/skeletonlabs-repl-gh962k?file=src%2Froutes%2F%2Bpage.svelte

More Information

This can be solved with the ::-webkit-scrollbar-corner CSS pseudo-element by styling it according to the current theme and mode.

Alternatively the following style could be used, that way the corner will just match the background color of an element.

::-webkit-scrollbar-corner { background-color: transparent; }

[brecht-vde]

I'm interested in giving this one a try if you think it's a good first issue.

[endigo9740]

Thanks for volunteering @brecht-vde - my only concern here is how this is handled with resizable elements, such as textareas. Those typically have a handle that should be draggable to resize. We don't want to obscure that in any fasion.

Also note we're in a bit of a transitionary period as we move from v1 to v2. If you wish to send a pull request, make sure to based your branch off of the v2 branch and add this to the core.css styles in our Tailwind plugin package found here in v2:
https://github.com/skeletonlabs/skeleton/blob/v2/packages/plugin/src/styles/base/core.css

I'm going to also ping @AdrianGonz97 to ensure this is the correct location. I believe he was looking to modify the location of the Core styes recently. Just want to make sure I'm pointing you in the right location!

[endigo9740]

This was resolved in v2