There's no way to require it. The best you can do is tell the user to do it.
Also, it use require.main.require instead
How do I create a plugin that puts CSS in the forum?
@שמח-לעזור it’s part of the ACP. Go to ACP > custom content > custom CSS/LESS
Put your css code there
@dunlix I want it as a supplement
@שמח-לעזור What do you mean? you can put whatever code you want in that page. If you want presets you can select a skin or theme.
@dunlix I want to have a plugin that puts CSS in the site
@שמח-לעזור you want to make it yourself? If so I don’t know how to make plugins.
@dunlix Yes I want to make my own
@שמח-לעזור This is not good I do not want anyone to be able to add but create my own plugin that has CSS in it