I wont to be able to change css with a single click

for example change size of letter size on a web

[OddDog]

I am sure I have seen this somewere, adn it was a great idea.

Any pointers?

[WibbleWobble]

Sure, Alistapart, wired.com and alltheweb to name three resize fonts with a styleswitcher.
Alistapart has two articles on it, and we've discussed it here before, only I can't find the thread. It couldn't have been more than two weeks ago, and it documented asp [roselli.org] / php [alistapart.com] and js [alistapart.com] versions of css changers/styleswitchers.

I don't know much about it frankly. There were some simple php instructions for random and daily changing styles in the previous discussion, if someone can root it out.

[OddDog]

thats great thank you!

[ricfink]

The most-used styleswitching technique (based on what I've seen and I've really looked) is the one that's featured in an article by Paul Snowden in AListApart.
You can see it in action at the devedge netscape site as well.
It uses the W3C HTML 4.01 Recommendation regarding "alternate stylesheets" to download one or more stylesheets along with the document and then allows you to activate one at time using a javascript "switcher".

There are other ways to switch stylesheets, as well.
Check out thread
[webmasterworld.com...]
for an explanation of at least one of them.