If programmers use someone else's code for text shadows etc, are they required to ask permission or give her/her credit?

I would agree, it's okay in this example. If you're copying some functionality, than you may need to reconsider. They may ask you credit them in some way, in which you would follow.

But I've done things like copy the padding used on a button from another site, because I liked it's size. Or copy what particular color of green, because it's a pleasant green to look at.

A lot of these moral questions can be answered by switching shoes. If it was your text-shadow code, what would you want someone to do if they copied it. Me, I can morally say nothing, to be honest. It wouldn't bother me.

But if I wrote code that say morphed a submit button into some cool, fancy animation while it was submitting, and that transformed into a success or failure icon..and I didn't specificity put that code out there to be found, you just stumbled acrossed it, I might not be as happy if I found out you took it. However, if you emailed/tweeted me saying you loved it, and wanted to know if you could use it, 99% of the time I'd say absolutely yes, have at it, just because you asked.

Us family of developers are pretty sharing, and giving individuals, just treat us, and our code when decency and respect, and it'll be a-ok.