As surfaced in mui/material-ui#40332, there seems to be a bug with the focus treatment for the Slider component.

• Suppose the focus styles are added to the thumb slot using our workaround class Mui-focusVisible through ${sliderClasses.focusVisible}. In that case, the problem is that they persist even if you move away from the thumb after clicking, dragging, and leaving it. That's illustrated in this comment: [base-ui][docs] Polish the Slider demos material-ui#40332 (comment)
• If the focus styles are added using the native focus-visible pseudo-class instead, the above-described behavior does not happen anymore. However, the problem then is that none of the styles appear if focusing/targeting the Slider's thumb using the keyboard.

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