A few references for styling buttons with CSS. I'll also point you to a couple CSS frameworks.
If you're having trouble getting your button styled just right, perhaps begin with one of these generators:
If these helped you, then perhaps you would benefit from checking out a CSS framework. There are a handful out there, but the most popular seem to be Bootstrap and Foundation.
A brief description of CSS, before suggesting a couple free courses.
A cool tool for converting back and forth between RGB and HEX values.
The golden rule of absolute positioning.