How do I apply multiple CSS classes to a HTML tags when website designing?

Applying the website design classes

To use more than one class inside the HTML tag in the  class attribute, simply use both separated by whitespace. For example this uses two classes called class1 and class2.

<div class='class1 class2'>
    Your website design code
Defining the website CSS classes
To have some CSS restricted to when these two classes are found together in the class attribute with an HTML tag simply combine them like this
.class1.class2 {
     Your website design CSS...