CSS multiple classes property override

Just wanted to throw out another option in addition to !important as well as style definition order: you can chain the two together as well:

.myclass.myclass-right{float:right;}
.myclass{float:left;}

As long as the selectors have the same specificity (in this case they do) and .myclass-right style block is defined after .myclass, yes.

Edit to expand: the order the classes appear in the html element has no effect, the only thing that matters is the specificity of the selector and the order in which the selectors appear in the style sheet.

Using !important is one way to do it.

.myclass-right{
    float:right !important;
}

In addition if you are more specific with your selector it should override as well

div.myclass-right{
    float:right;
}