Invalid at computed-value time

A var() result that doesn't make sense falls back to inherit/initial.

What does invalid at computed-value time mean?

A declaration using var() can only be checked once the variable is filled in. If the result makes no sense, the property falls back to its inherited or default value instead of the next rule.

:root { --size: blue; }
.box { width: 300px; width: var(--size); }   /* invalid: width becomes auto, not 300px */

Level: Master · More CSS terms at this level

Updated September 27, 2026