Unable to determine the button styles for the Zen theme.

Hello. I am currently theming a site based on the Zen theme. The problem is as follows. In the Zen theme (or even in the CSS files of Drupal itself), there are form buttons that look like this:

And this is how it looks when it is in the hover state:

Question: where are these styles located? Firebug does not find anything substantial, such as: the image on hover, the border, what color it is, etc. From the box model, I can see border: 3px, padding: 0 6px; But this is extremely little to make the buttons for other elements of the site look the same. I can guess that the styles of these buttons originally come from the HTML forms themselves (I know the basics, but I learned it a long time ago, and nothing about buttons seems to have come up). I don't want to guess by eye and try to figure it out using my own styles. I would appreciate any advice and tips.