Forms and CSS
If I were to write an article about using CSS with forms it would be something like this. In essence - don't style field elements in any way that alters the appearance that users are used to. This is a rule you learn by experience. It's easy to make fancy-looking fields on a form. What's not so easy is to ensure the user knows it's a field.
The article also talks about using other, form specific, elements - fieldsets, legends and labels. If you don't or haven't used them yet, have a go, they can bring extra style and functionality to a boring looking form.
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I noticed, with regards to this specific point, that if you just prepend an x (or delete) to anything Topstyle shows as Red, you're actually a long ways to good practices for styling. :-) All of the style attributes for tweaking inputs show red under CSS1 rules in Topstyle.
Actually I think as long as they resemble the boxes that browsers draw by default you can play with them a little. Yes I agree changing them to lines (like a paper form) or other such things may confuse. I've been guilty of it in the past and it hasn't worked. BUT, I style them to indicate requirement and validation which works well I think.