There is a html page customized with css styles(I cannot change this css). One tag of this page designed as a container for dynamic html data. How can I “reset” css settings for this div(css styles defined in the page have no influence on the content of this div)?
I have access only to dynamic html and I can add more css styles to a page.
If I understand you correctly the problem you have having is that the CSS for the main page is affecting the CSS for your “dynamic” div. For the most part there is nothing you can do about that, other than specifying higher-priority styles to the dynamic content you are loading.
You can do this by doing in-line css, or by doing other more specific CSS declarations in a file or tags.