Oh yeah.

Keyboard focus and focus indication on browsers is fundamentally broken.

We often notice when focus is buggy. But there are many many hidden/unobvious edge cases.

Previously I created a fix for the worst focusing issues on browsers by creating a fully custom framework (before modern HTML help with popovers/dialogs/overlays/viewports/anchors). No other framework at the time managed Internet Explorer's quirks very well (we served businesses who mostly used that browser).