fix broken theme CSS links in the website

[lapla-cogito]

Currently, some parts of the website's CSS are not being applied. This seems to be due to a broken link to the originally referenced CSS. I suspect rust-lang/mdBook#1368.

changelog: none

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[BenoitZugmeyer]

👋 Hi there, I just bumped into this issue and I was planning on submitting a PR. Using raw.githubusercontent.com won't work because files are served with Content-Type: text/plain and the browser will refuse to apply the style.

A potential solution could be to use jsdelivr.net like so:

    <link rel="stylesheet" href="https://cdn.jsdelivr.net/gh/rust-lang/[email protected]/src/theme/css/variables.css"/> {# #}
    <link id="styleHighlight" rel="stylesheet" href="https://cdn.jsdelivr.net/gh/rust-lang/[email protected]/src/theme/highlight.css"> {# #}
    <link id="styleNight" rel="stylesheet" href="https://cdn.jsdelivr.net/gh/rust-lang/[email protected]/src/theme/tomorrow-night.css" disabled="true"> {# #}
    <link id="styleAyu" rel="stylesheet" href="https://cdn.jsdelivr.net/gh/rust-lang/[email protected]/src/theme/ayu-highlight.css" disabled="true"> {# #}

The version could be omitted to resolve to the latest one, although I would discourage it as things might break in the future.

See jsdelivr docs.

[lapla-cogito]

@BenoitZugmeyer Thanks for your comment! It looks like I assumed that type="text/css" was already present in each tag. So, as a fix, I considered adding the type attribute or loading these stylesheets via a CDN, as you mentioned. Since the latter option makes more sense, I went with that. Thanks again!

[Alexendoo]

Thanks! Having them be versioned is great

[eric-seppanen]

I suspect this caused css to be broken for all versions of the lints except master.
See #14494.