Do not start CSS pseudo-class names with numbers

When newbies develop div+css, they need to name the CSS pseudo-class names, such as .ggg, #ccc, and other formats. However, some novices often want to keep things simple when naming CSS pseudo-classes, so they directly use numbers to name them, or name CSS pseudo-class names starting with numbers. This is not allowed.

Newbies should be aware not to name CSS pseudo-classes starting with Arabic numerals, otherwise the browser will not be able to interpret and parse CSS classes named starting with numbers, which will eventually cause incompatibility with similar CSS hack styles, or classes with CSS names starting with numbers will be invalid (the browser cannot interpret them).

Of course, it is okay to use English letters plus numbers to name, but remember that you cannot use numbers plus letters or pure numbers to name CSS selectors. I hope newbies will pay more attention.