Advice styling html.Button with CSS?

Working through CSS attributes on my own app, the hardest part for me is figuring out what to do with how the Buttons look by default. Is there a style guide anywhere on editing the CSS for html.Button (since it’s not immediately obvious how), or does anyone have any advice on generally making them slightly bigger and nicer?

I know one can change the font of the button through 'font':'16px Arial...', and have the box around it grow bigger, but then the box takes on a gray background and it is not rounded anymore the way it is rendered on my firefox.

You can change the colour of the button like this: