Looking for help to find/create custom css.

I read alot of layout topics here, wich are very good and detailed how to change something. But... My own custom.css is not overwriting the css from sermonspeakers. I read that i need to copy/overwrite the file. Might be little edgy, as I noticed there isnt any css or view folder to make a duplicate...

I am kind of out of ideas.

Try adding !important to each css seting in your custom.css file that you are trying to overwrite. Its not prefered way but it gets the job done. also custom css file will be located in templates/{your template name}/css folder.

If you can get me a link to your site, I can have a look why it doesn't override properly.
It may be that the template doesn't load the CSS files in the proper order, or that your selector isn't specific enough.
What Andrei proposed will most likely work, but isn't the most elegant way (as he said).