Validators for HTML and CSS

I am extremely new to HTML and CSS, sticking my toe in before the big splash so to speak Do Sheet Authors use any Validators on their HTML and\or CSS code? Are they useful? If you do use them in some way, do you recommend and specific one?? I have tried several and I get many Warnings and Errors (not always the same ones from each site's tools), on existing character sheets. Thanks, as always, for any help provided. Mike

I use some online ones if I've seemed to have broken something major, but as you have noticed they spit out error-messages on functioning code too. IMO they have limited utility. I don't have any specific to recommend, I use more than one when I use one. Don't actually remember if I've caught anything major with them. Someone more experienced might have a differing opinion.

Thank you Andreas. For me it is 'Information Overload' with them. Code 601 - Andromeda Strain, -lol.