if you want to make your site looks like some other sites, you’ll need to change the css as well as HTML too (if I’m getting you right).
The easy way is to get the HTML & CSS of the site which you really like then convert that static html/css to wordpress theme.
If you’re talking about a little portion/section of your website to looks exactly or somehow the same as another site you like, you should first copy the html to that specific section and then apply the css by writing the css to your style.css.
