It depends oh what you want to do, really. If you don't enjoy working in the frontend and you don't do it to earn a living, you don't need to touch any of those topics.
If however you want to apply for fullstack developer jobs, it sort of makes sense to know what's going on with HTML/CSS/JS. So let me turn the question around for you: Why do you think you need to learn HTML/CSS?
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It depends oh what you want to do, really. If you don't enjoy working in the frontend and you don't do it to earn a living, you don't need to touch any of those topics.
If however you want to apply for fullstack developer jobs, it sort of makes sense to know what's going on with HTML/CSS/JS. So let me turn the question around for you: Why do you think you need to learn HTML/CSS?