Ok, let's take a look at how, by adding some simple code to your child theme or custom css, you can improve the appearance of your site and make it look unique.

Your theme's stylesheet governs, among other things, fonts, font sizes, font color, line height, h1-h6 headings, etc. To change these from the original, you will need to change your stylesheet accordingly.

If you are using a test site, which I always advise if experimenting with a theme, you can modify the stylesheet directly (although not recommended), as if things don't go to plan no damage has been done. If you are going to do this to a published website, as mentioned previously, it is advisable to create a child theme or install a custom css plugin, any changes can then be made to the child theme or custom css, leaving the parent stylesheet "as is".

I have seen so many websites, apart from the niche and content, that are identical in appearance, with the same banner head, font face and size, and headers exactly the same apart from the wording.

In this first example I have used the Twenty Thirteen theme as an example of, and it's just my opinion, of everything a theme shouldn't be, with oversized headers and undersized text. (We'll change these in the next example).