How to edit the CSS for a section of OC?

Hello,

Using v1.5.1.3.

I just want to know how to edit the CSS for a section of OC…

For example:

There are three parts…

1) Header (at top)
2) Middle (below header and above footer) I call it main content.
3) Footer (at bottom)

I can edit the look of header and footer using the stylesheet.css file, but how do I edit the general look of the Middle?

Many thanks in advance,

Actually the slideshow part and the featured part is treated as a module that belong to the module folder
you can edit the slideshow.css file catalog\view\theme\default\stylesheet
for the featured part, if you look at the \catalog\view\theme\default\template\module\featured.tpl
you can find that part is inside <div class="box">,<div class="box-content"> ...etc
you can search the corresponding class at catalog\view\theme\default\stylesheet\stylesheet.css to make modification
I am new to opencart hope this is what you want

Is there a cache somewhere I need to empty inside the OpenCart system? I'm changing the CSS and nothing is happening in the live store?

depends on, if you use by example a custom Page Cache Extension, but usually, it's done by
cleaning out the vqmod/vqcache/... Section in OC v.1.5.x Versions.
Ernie