"screen readers" is quite reductive, as there are other assistive technologies. content hidden this way is even announced by things like Alexa/Siri etc, so it's not so much just "screen readers".
in the long run, we may even consider changing the actual classnames (maybe `.visually-hidden` / `.visually-hidden-focusable`, though admittedly that's a bit verbose).
also includes a tiny tweak to layout.md to generalise the note about using `.sr-only`
- Use a semitransparent gradient from light to dark which works on any background-color
- Store the gradient as a custom property (--bs-gradient)
- Remove `.bg-gradient-*` variants in favour of `.bg-gradient` which works even when `$enable-gradients` are enabled
- Add gradients to navbar, active page links and badges when gradients are enabled
