Possible to clean up CSS in all templates?

Last year I attempted to set up zencart and do some customization. But after a few times, I gave up till recently I decided to try zencart again.

It got better but now I am struggling with cleaning up css in all templates especially when I am writing my own stylesheet from scratch, instead of stylesheet.css.

I wanted to cut many divs on the pages. For an example on the page source, after I place div class="navCategories", I see other class (category-top):

<div class="navCategories">
<ul>
  <li><a class="category-top" href="/index.php?main_page=index&cPath=11">Women</a> </li>
  <li><a class="category-top" href="/index.php?main_page=index&cPath=8">Men</a> </li>
  <li><a class="category-top" href="/index.php?main_page=index&cPath=7">Babydolls</a> </li>
</ul>
</div>

OR

if I place div class="sidebarLeft" on main_page template, I see some classes or ids:leftBoxContainer, categoriesContent and sideBoxContent.

I tried to look around in /includes folder but couldn't find the classes or ids that I want to delete and add my own styles. Because most of the templates I came across have all code stuffs that did not show any of the styles that are shown on view source.

So I am wondering if there is any way to go in templates to remove styles and replace them with my own styles?

If there is, please give me directions.

Thank you for your time in advance.

The classes and tags are defined in the code
This is only so that they can be addressed by the css if additional styling is required,
They are like addresses where elements that live there can be altered through css.....no addresses then no way to control style.
You are trying to do something that is not necessary
Why rename what already exists