CSS不适用于嵌套的子div

I have a few nested divs on a website I am creating with the Joomla engine. The problem lies mainly in the fact that the plugins themselves nest 2 divs inside my already created div "banner", meaning I do not have access to these two divs. Within them is the small, rectangular image. This image should help you see my issue (I'd post an embedded image but you know, apparently I need 10 rep):I have a few nested divs on a website I am crea