Be careful using those "random-style" css classes like .gmYgTL and possibly .sc-AxgMl. It seems that the class names can change between Joplin versions. So you could upgrade Joplin and this would stop working. You would then have to find the new names for those classes and edit your userchrome.css. You would then have to do the same after the next upgrade and the next etc.
It would also mean that someone not using the same Joplin version as yourself could not use this.
@laurent 's suggestion (see link) is to stick to using "traditional" selectors for a better chance of version to version stability.