Improve Compatibility with Darkreader

[emmahodcroft]

See email to hello@nextstrain from Henri on 3rd Feb 2020.

Some with low vision benefit from inverting website displays, so they have a black background and white text. Extensions like Darkreader aid with this.

Using Darkreader with nextstrain.org/ncov renders like this:

Mostly ok - but the tip labels on the tree don't show up at all. The mouseover still works. I suspect this may be because the tree is rendered slightly differently from the rest of the page, so isn't responding to however this works?

Would be good to test a little more thoroughly to ensure everything else is working, too.

[jameshadfield]

Tip labels are SVG text, which would be my guess at why they're not inverted.

[joachimschmidt557]

This issue has been raised before with DarkReader. See https://github.com/darkreader/darkreader/issues/1963

The solution there was to create some exceptions for the site in question, ngrok.com.

This could also be achieved on nextstrain.org with:

.tipLabel {
    fill: #e8e6e3;
}