float style in external css

[Z1P2]

This may be a stupid question, but I have ran a forum for a while on a free host and used the float styling inside the image tags to style images in the posts. Due to excessive spam and a lack of tools to fight it, I'm now moving my forum over to a phpbb forum (located at www.GeneralAquaria.net) which does not support css styling of things like that from inside the posts. However, I have determined that I can use classes to call a style from the phpbb's css style sheet. So I am wondering if it is possible to use the style="float:right;" in an external css on a class?

If so, what would that look like?

[drhowarddrfine]

Any CSS styling property can be used on any class.