> I think we should probably focus on integrating this logic (adding the selected class/hiding panes) directly in the tabpanels custom element and the CSS into toolkit/content/xul.css I could only find one other use of `<tabpanels>` though, in [browser.xhtml](https://searchfox.org/mozilla-central/rev/b2433a832c250c55255e0ee37d05192d04f20427/browser/base/content/browser.xhtml#2369), and that one probably requires a bit more attention for performance reasons so we might want to use something other than grid layout there. Like abs.pos. blocks for the panels. But yeah, we can add the suggested styles here to xul.css and let each consumer override the styling as they see fit I guess.
Bug 1690357 Comment 2 Edit History
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> I think we should probably focus on integrating this logic (adding the selected class/hiding panes) directly in the tabpanels custom element and the CSS into toolkit/content/xul.css I could only find one other use of `<tabpanels>` though (apart from tests), in [browser.xhtml](https://searchfox.org/mozilla-central/rev/b2433a832c250c55255e0ee37d05192d04f20427/browser/base/content/browser.xhtml#2369), and that one probably requires a bit more attention for performance reasons so we might want to use something other than grid layout there. Like abs.pos. blocks for the panels. But yeah, we can add the suggested styles here to xul.css and let each consumer override the styling as they see fit I guess.