The properties of a second class will override those already set. There is no need to use !important here.
For example:
.red { background-color: red; }
.background-none { background: none; }and
<a class="red background-none" href="#carousel">...</a>
Credits: https://stackoverflow.com/questions/20954715/how-to-override-the-properties-of-a-css-class-using-another-css-class#20955958