Html Question Where Should I Post It?

Hi guys, I had this question, but I wasn't sure if this is the right place to post. I develop websites and have a few domains that basically have the same exact content for now. But somtimes I want to make changes to the main site and then have the other sites with the same content change without me having to reupload the HTML files. Is there a way to do this? I'm not sure if this is something I could do with CSS STYLE SHEETS.

thanks,:wave

 

THANKS! :wave

 

:wave and welcome aboard..