There are levels of fundamentals though, since parent mentioned HTML/CSS/React I guess they're referring to being able create a layout by hand vs using a CSS fr

There are levels of fundamentals though, since parent mentioned HTML/CSS/React I guess they're referring to being able create a layout by hand vs using a CSS framework/library. You don't need to know how a CPU works to fix a CSS issue, but if all you know is combining the classes available you'll have trouble with even the simplest web development. Everyone should know enough fundamentals to be able to write simple implementations of the frameworks they depend on.