Stage 1: The page can be created without thinking about browser compatibility issues, but the page is written using TABLE mode DIV everywhere.
Stage 2: Compatibility problems are thought of, but they cannot be prevented in advance. They can only fix the problems and use HACK technology extensively.
Stage 3: BUGs can be prevented in advance, but ID and CLASS are widely used in the style sheet, and CSS is translated into overlapping style sheets, such as "DIV P SPAN". This code marks the sub-element SPAN of P in the sub-element of DIV. By writing this way, you can define the style of SPAN without adding CLASS to SPAN. This is the advantage of CSS. Why not make good use of it and be sure to define a CLASS!
Stage 4: This stage is the most difficult, good HTML semantic structure, reasonable CSS, and reusable styles. There are articles about good semantics and reasonable CSS in this area. I will definitely write a special topic to study these two aspects in the future.?