I see no reason why a backend web developer wouldn't know html/css and pure js to an acceptable level. You don't have to be a Node.JS ninja on the frontend but

I see no reason why a backend web developer wouldn't know html/css and pure js to an acceptable level. You don't have to be a Node.JS ninja on the frontend but definitely have a good grasp of what's going on on the frontend. People who can only do one thing will have a harder time leading teams or going to management.