Exhibit A: CSS centering.
Exhibit B: The so-called "Holy Grail" layout. [^1]
This is really out of date. Even IE11 supports flexbox. It is trivial to center things both vertically and horizontally, and easy to make a “Holy Grail” layout.
If you don't need to support IE11 you can use CSS Grid and do the entire layout in one or two CSS properties.
I disagree completely. It's easy to get a 'hello world' type thing working in HTML, sure, but it's very hard to make something behave like you want. Traditional UI toolkits are much simpler and easier to understand.