Templates and CSS

If familiar with the layout, I can see how CSS is the number one application to style web pages using HTML. You can adjust almost everything from colour to font to positions of borders and just generally the entire layout of your page.
My understanding of templates ( and correct me if i'm wrong) is that they are already premade and stylized so that all you have to do is pick a layout or colour instead of manually doing it through html. The advantage of this (for me and other thats aren't too keen abusing css) is that its simple to use, however the disadvantage is the limited choices it has.
Using both CSS and templates, I altered my blog's font, colour, borders and size. Depending on where I felt confident enough to change my page using CSS I did, however I still very much lean towards the templates.
I also found that accessibility in a web page is subtle but effective. Such as larger font and bolder colours for the visually impaired, or audio for the hearing impaired.

I find CSS challenging, however would like to become more familiar with it!
good day!