Moving used flat-ui properties to my css file

I am working on a project which is a web based software. This project is probably the most in-depth I've ever been with html, css, js, and other accompanying languages.

I'm using bootstrap with flat-ui and my own css file to make it the way I want. I understand how the file reference works with bootstrap first and then flat-ui and then mine but my question is, should I move what css properties I used from flat-ui to my own css sheet.

An example of this is from the flat-ui css file, I am using the property
Should I copy this properties into my own css file? Doing this would keep the number of css files down to 2 and would be easier to mange. I am just unsure if this of good participate or its a no-no since I copied the code from a file I did not generate.

Thanks everyone! :)