Broken style: ref-header

[jeff-matthews]

Bug report

I just noticed this, but the style appears to be broken. I'm not sure how long it's been this way because we haven't had any reports. It probably happened recently during branding updates for the theme, which included some spectrum CSS upgrades.

Background

When we implemented MD linting in devdocs, we were forced to create a style called ref-header to act as a pseudo heading for the "Related topics" section at the bottom of some pages on devdocs.

The motivation was to have a heading that stands out but doesn't appear in the "On this page" navigation on the right side of each page. Using the no_toc class was not a viable option because it violates MD linting rules.

[jeff-matthews]

I just ran a local MD lint test, and it appears that there's no longer a failure on the following:

## Related topics
{:.no_toc}

So we wither need to fix the style or remove it and replace all references to it in devdocs.

[jeff-matthews]

This style is actually defined in the devdocs project, not the theme.

https://github.com/magento/devdocs/blob/master/src/common/css/devdocs.css#L15