data-ms-bind:class

This feature lets you add a class to one or more elements on your published site.

This is especially useful when you want to change the logged-in member experience without needing to duplicate your members only area for each member type. 

1) The Attribute

data-ms-bind:class="your-classname"

Alternatives

If you would prefer to add styling without creating additional classnames you can use the data-ms-bind:style attribute instead.