Collapsed sidebar looks odd in the new design

[jg2]

Hello, just got this new 'nova' design thing, I don't hugely mind the rounded corners and colors and all that, but this is unpleasant to look at: 

 looks like this in the default theme, slightly more subtle:

I don't really get why the collapsed sidebar would have a different color anyways – when it's not collapsed it's the same color as the top chrome and looks just fine. Could this be changed?

[dftf]

Until it gets fixed, you can choose to reverse the new Nova UI changes:

In the web-address bar, type about:config
Press ENTER/Return
Accept any warning, if shown
In the search-box, type nova
Double-click the line "browser.nova.enabled" to change the value from "true" to "false"

[jg2]

I've found now that there are some themes that don't have this problem, one called 'Proton' for example, which is also pretty decent.

Would be nice if the default themes were fixed eventually to look well in all configurations though