How to Change Header Icon Color?

I have a similar problem as the OP, probably somewhat simpler: For some reason the colour of the header icons got darker for no apparent reason (I assume it was related to the tidy-up measures on your side). Since my header is a darkish, I want the icons brighter.

I tried this

and am happy with the result. But I can’t seem to figure out how the hover settings work. With only the above css, my hover looks like this:

So the icon turns grey again, which is okay, but I’d like to try some other tints on it. The background seems to turn white (or almost white), which I would like to change to make it coherent with other menus.

I tried

.d-header-icons .d-icon:hover {
   background-color: #b0cee8; 
   color: #fff;
}

but it gives me this:

How do I get the whole box to change color? And I don’t understand why the icon itself doesn’t stay white…

And while I’m at it: My new topic button also suffered. The colour of the + icon is no longer the same as the text:

image

My CSS for the button is (and has always been):

@import "common/foundation/variables";

#create-topic {
    background-color: $tertiary;
    color: $secondary;
}

#create-topic:hover {
    background-color: $tertiary-high;
    color: $secondary;
}