Also https://drafts.csswg.org/css-overflow-4/#scrollbar-gutter-property

Scrollbars are also one of the things that still need vendor-specific selectors if desired to be customized.
It would be great if we could unify those one day.

There hasn't been movement on this in a while so I'm going to close this but put it on the backlog.

I would like a Custom Scrollbar.

So that the Scrollbar could use for example decorators like in VSCode, adjust a different action for e.g. onmousedown button===1 on individual elements of the scrollbar, add additional elements inside the scrollbar using the shadow house.
Such Custom Scrollbar would be automatically added to all or specifically selected by the developer.

Just adding CSS styles is definitely not enough.

Based on https://drafts.csswg.org/css-scrollbars/#out-of-scope I'm unsure there's much value in looking into scrollbar customisation as part of Open UI efforts. scrollbar-color and scrollbar-width should provide enough for most design systems to be satisfied with. There's also been some movement to actually implement them in WebKit and Chrome (admittedly that movement is from me), so these should actually be interopably usable soon.

There hasn't been any discussion on this issue for a while, so we're marking it as stale. If you choose to kick off the discussion again, we'll remove the 'stale' label.

Closing this based on a rough agreement of what @lukewarlow said above.