HTML

html add two classes

<a href="#" class="class1 class2">My Text</a>

html multiple class

Multiple Classes
HTML elements can belong to more than one class.
To define multiple classes, separate the class names with a space,
e.g. <div class="city main">. 

The element will be styled according to all the classes specified.

css assign multiple classes to one element

To specify multiple classes, separate the class names with a space,
e.g. <span class="classA classB">.
This allows you to combine several CSS classes for one HTML element.