Improve universal stylesheet served to old IE browsers

[alexgibson]

Description

The universal stylesheet we serve to IE8 and below could benefit from some minor tweaks to make it a bit more readable:

1. The navigation contains many links, which pushes the main page content down a long way. We could provide a really basic layout for this so that it doesn't take up so much height.
2. Hide the useless <button> elements (e.g. "Menu", "Close Firefox Menu"), that don't do anything without the JS.
3. Improve readability by placing all content within a centered container in the page and a set max-width.
4. Hide content that is only really meant for Firefox users.
5. Anything else?

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💛 Success Criteria 💛

• Browsing the no-frills site is a slightly more pleasant experience.

Tasks

• Update legacy IE stylesheets.

[hoosteeno]

@alexgibson do we know enough about this to estimate the effort of it?

[alexgibson]

@hoosteeno probably a days work, possibly a 3 (Assuming this is just an engineering task. If we want design input then this could grow).

[alexgibson]

This is now up on demo at: https://bedrock-demo-agibson.oregon-b.moz.works/

Screenshots for those without VMs:

Homepage before & after:

/firefox before & after

/accounts before & after

/channel before & after