If you have ever tried writing CSS for your HTML with lots of boxes called <div>’s you will find that the padding, borders, and margins are notoriously difficult to get right in a lot of circumstances. The model is basically what is called broken in programming parlance, its not logical, and it is not normalized. It can waste hours of time in learning HTML layout and hours when modifying and existing pure HTML/CSS web site.
The other problem with both HTML and CSS are the lack of inheritance, meaning you have keep repeating yourself and each time you make a modification you have to remember to do it in every case that you have used or worse in cryptic CSS code left by a pervious coder.
