Which page to amend default blog page HTML

Hi,

I’m looking for some help to amend the HTML on the default blog page within WordPress.

Basically, we are using DIV inserted boxes throughout the theme and all pages created so far are fine with exception to the page which displays blogs in list order (website.com/category/blog/)

We are using a transparent background to allow inclusion of the boxes but we are struggling to find which page to amend in the theme to get post precis to display within boxes rather than a transparent background.

We have sorted the ‘post’ page for each individual blog, it’s just the one which shows the precis of individual blogs.

Sorry if this doesn’t sound clear, hopefully someone will know what I’m trying to do..

thanks

RichyP