It doesn't look quite right, because the lines are too far apart,
and it's not going to be announced by screenreaders as a menu button,
since that's not what the symbol means.
This adds a real tooltip and uses a better drawing of the icon.
This is a redesign of the feature, with parts pulled from
https://github.com/rust-lang/rust/pull/119049
but with a button that looks more like a button and matches the
one used on other sidebar pages.
Fixes the desktop scrolling weirdness mentioned in
https://github.com/rust-lang/rust/pull/98775#issuecomment-1182575603
As described in the MDN page for this property:
* The current Firefox ESR is 102, and the first Firefox version
to support this feature is 59.
* The current Chrome version 112, and the first version to support
this is 63.
* Edge is described as having a minor bug in `none` mode, but we
use `contain` mode anyway, so it doesn't matter.
* Safari 16, released September 2022, is the last browser to
add this feature, and is also the oldest version we officially
support.
Michael Howell