Hello
1. install firebug in firefox
2. open the desired web-page, right click with the mouse on the element and select "Inspect Element"
3. copy the CSS rule in any CSS file of you joomla template
4. prepend
body to the rule to make it of higher precedence
5. change the rule CSS styles to match your needs
these are described in our FAQ article:
How to customize CSS styles of FLEXIcontent
Regards