I have some stylesheets from different sources in my web project. I want to harmonize them. Some styles I need from the one, some from the other. Is there a tool or method how
If you view the site in FireFox, and use the Firebug extension, you can then look at each element in your rendered page, and by using the "CSS" tab in firefox, you can see the cascade of style rules that are being applied to that element, and from what CSS source file each came from. It will show you what rules are being overridden, too.
This is helpful in determining just where each particular rule is coming from, and what is being overridden.
You still have the task of "rationalizing" your style sheets, and there may be other tools that can help in that.