Reference another property value from the same containing block. Restricted to referencing properties that don't already reference other properties. this( *property-name*, *fallback* ) ## Parameters * *`property-name`* Property name * *`fallback`* A CSS value ## Returns The referenced property value, or the fallback if it has not been set. ## Examples ```css .foo { width: this( height ); height: 100em; } ``` ******** ```css /* The following both fail because they create circular references. */ .bar { height: this( width ); width: this( height ); } ```