rustdoc: unstable feature warning wraps early on iPad

[jsha]

Visiting https://doc.rust-lang.org/nightly/std/mem/union.MaybeUninit.html#method.assume_init_read on an iPad Pro results in the following:

The yellow box warning about an unstable feature is both too long and too short. If it were wider, it could accomodate all its text without wrapping. Given that it wraps, it shouldn't be so wide.

This reproduces on latest Chrome, Brave, and Safari on iPad, in landscape mode. Note that in landscape mode it looks fine. Also, the width of the yellow box in landscape mode is exactly the same size as when it's in portrait mode.

Reproduces on stable as well as nightly.