How to apply two CSS classes to a single element

Question

Can i apply 2 classes to a single div or span or any html element? For example:

aa

I tried and

Answer 1

1) Use multiple classes inside the class attribute, separated by whitespace (ref):

aa

2) To target elements that contain all of the specified classes, use this CSS selector (no space) (ref):

.c1.c2 {
}