Previously, tidy-html5 (`tidy`) would complain about a few things in our
HTML. The main thing is that `<summary>` tags can't contain `<div>`s.
That's easily fixed by changing out the `<div>`s for `<span>`s with
`display: block`.
However, there's also a rule that `<span>`s can't contain heading
elements. `<span>` permits only "phrasing content"
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/span, and
`<h3>` (and friends) are "Flow content, heading content, palpable
content".
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/Heading_Elements
We have a wrapping `<div>` that goes around each `<h3>`/`<h4>`,
etc. We turn that into a `<section>` rather than a `<span>` because
`<section>` permits "flow content".
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/section
After this change we get only three warnings from tidy, run on
struct.String.html:
line 6 column 10790 - Warning: trimming empty <span>
line 1 column 1118 - Warning: <link> proprietary attribute "disabled"
line 1 column 1193 - Warning: <link> proprietary attribute "disabled"
The empty `<span>` is a known issue - there's a span in front of the
search box to work around a strange Safari issue.
The `<link>` attributes are the non-default stylesheets. We can probably
refactor theme application to avoid using this proprietary "disabled"
attribute.
That means it will be visible under "Implementors" on trait pages, and
under "Implementations" on struct/enum pages, even when all methods are
collapsed.
Switch to a float layout for rightside elements.
