CSS :only-child Selector

Specify a background color for every <p> element that is the only child of its parent:

p:only-child {
background: #ff0000;
}

Definition and Usage

The :only-child selector matches every element that is the only child of its parent.

Version:	CSS3

The numbers in the table specifies the first browser version that fully supports the selector.

Selector
:only-child	4.0	9.0	3.5	3.2	9.6

:only-child {
css declarations;
} Demo