There are two types of buttons, Primary and Secondary. These buttons can be found in your Header menu with the Button element, the comments area of your single posts, and other areas of your website.
To customize the appearance of the buttons you can see the Buttons panel inside Customizer. There you will get two types of styles for the buttons: Filled and Outline.
The filled buttons have a background color and a text color.
The outline buttons have also a background color and a text color, but the difference consists in the fact that the text color will apply to the border as well.
Apart from colors, there are also padding controls (which can be customized according to each device: desktop, tablet, mobile) and border-radius.