How can I export multiple org files at the same time to HTML?

I have a structure like: ``` x.org x.html x.css y/a.html y/a.org y/b.html y/b.org ``` y is my subfolder and I import a and b from x using links.

I haven’t tried it myself before but I think what you want might be org-publish. https://orgmode.org/worg/org-tutorials/org-publish-html-tutorial.html