bug: "contents" button to make docs TOC appear broken at <1200px

[craigbox]

Up to 1200px, there is a floating "Contents" button which is missing its hamburger icon:

When you click it to expand the contents, you can't make the pane go away again.

[craigbox]

/cc @Arhell in case you fancy a look at this. I think for the Contents menu it's the same bug you fixed recently

[craigbox]

Actually, the cross is there on the main site, but not in my deploy preview for some reason

compare https://deploy-preview-16010--preliminary-istio.netlify.app/latest/docs/ with istio.io, which looks like this

[craigbox]

The problem seems to be related to SVG sprites and Chrome. It works fine in Safari. I tried adding href to the SVG template as well as xlink:href, as is required by SVG 2.0, and I also tried setting a doctype of SVG 1.1. Neither changed anything locally.