Bugzilla

With bug 1883896 in effect (`layout.css.h1-in-section-ua-styles.enabled=false`, default in Nightly only), the headlines on https://arstechnica.com have an odd spacing.

The headlines are a link inside an `h1`, and they do style the font size and line height of the `<a>`, but not the `<h1>`. With the old UA stylesheet in place, the rule that would set the font size was

```css
:is(article, aside, nav, section)
:is(article, aside, nav, section)
:is(article, aside, nav, section)
h1 {
  font-size: 1.00em;
}
```

That rule is now gone in Nightly, falling back to [the default `font-size` of `2em`](https://searchfox.org/mozilla-central/rev/b73676a106c1655030bb876fd5e0a6825aee6044/layout/style/res/html.css#168), which is what's driving the increase in effective line height.

We could easily ship an intervention containing

```css
body.mobile-view .archive-list li article.in-column h1 {
  font-size: 1em;
}
```

but given this is a change in the UA stylesheet, this could have a widespread efefct.

With bug 1883896 in effect (`layout.css.h1-in-section-ua-styles.enabled=false`, default in Nightly only), the headlines on https://arstechnica.com have an odd spacing.

The headlines are a link inside an `h1`, and they do style the font size and line height of the `<a>`, but not the `<h1>`. With the old UA stylesheet in place, the rule that would set the font size was

```css
:is(article, aside, nav, section)
:is(article, aside, nav, section)
:is(article, aside, nav, section)
h1 {
  font-size: 1.00em;
}
```

That rule is now gone in Nightly, falling back to [the default `font-size` of `2em`](https://searchfox.org/mozilla-central/rev/b73676a106c1655030bb876fd5e0a6825aee6044/layout/style/res/html.css#168), which is what's driving the increase in effective line height.

We could easily ship an intervention containing

```css
body.mobile-view .archive-list li article.in-column h1 {
  font-size: 1em;
}
```

but given this is a change in the UA stylesheet, this could have a widespread effect.