v6: <kbd> horizontal padding

[coliff]

I was thinking of making a PR for the v6 docs updating the keyboard shortcuts to use the more semantically correct <kbd> attribute but the styling of them didn't look quite right.

The css variables is --bs-kbd-padding-x: 0.25rem;

Perhaps could be increased to something like: 0.4rem and then it'd look neat (with a single character keyboard character appearing with a 1/1 aspect ratio.

[julien-deramond]

The rendering in your version is better for single-character <kbd>, definitely.

I played around with some CSS in this CodePen and added a min-width so single-character keys look always square.