Generally the three languages are mostly used to do most of the work (HTML, CSS, JS) [React is a framework], but you can consider some things like ejs, jinja, etc. which usually work with backend applications.
To gather more knowledge though, you can do some projects with multiple framework and try to use some Web APIs which can improve user experience.
Also you can work more on the topics which are asked to be kept in mind while making some product…
. (I don’t remember them all )
Have a good day