Adding Custom CSS to a Child Theme

Quick question regarding customizing the theme with CSS:

I have created a child theme and am adding custom css, here is an example:

This css only seems to work if I add it to the “Theme Options / General Options / Custom CSS field” and not my child themes “styles.css”

I assume this is because “main-options.css” is loaded after my child themes “style.css” and the “Theme Options / General Options / Custom CSS field” is loaded after everything else?

I am a bit new to all this and would like to know the best method for customizing the site with my own css.

Thanks and Minicorp is a great theme!