So out of curiosity (as I've not heard of it before) I installed a VM of archlabs with dwm and installed the same AUR package as you, added the CSS and it works just fine.
I would check the following:
-
Double check you are editing the right file in the right place - open the profile dir from Joplin (Help > Open profile directory) and check the userchrome in there is the same one as is being opened from
Options > Appearance > Custom stylesheet for Joplin-wide app styles. It should be in~/.config/joplin-desktop. -
Open Joplin and go
Help > Toggle development tools.
See this thread I posted before for a better description but basically press the little "arrow in a box" icon in the top left of the dev tools and click the editor button you are trying to remove.
You should see something like this:
In the elements section.
In the styles section at the bottom you can see the actual styles being applied - as I can't emulate yours exactly I applied a red border to my button which is being overwritten (as shown by the strikethrough) but you can still see that the CSS was valid and it would apply it if it wasn't being overruled.
Check to see if you have anything like that in there for the same selector but with display: none.