CSS contains zero unit declarations
This means that the URL in question is a CSS file that contains one or more zero unit declarations.
Why is this important?
The value of 0 works without specifying units in all situations where numbers with length units or percentages are allowed. There is no difference between 0px, 0em, 0%, or any other zero-value. The units aren't important because the value is still zero. CSS allows you to omit the length units for zero values and still remain valid CSS.
What does the Hint check?
This Hint will trigger for any internal or external CSS URL which contains zero unit declarations.
Examples that trigger this Hint:
The Hint would trigger for any style sheet that contains a zero unit declarations:
How do you resolve this issue?
It is recommended to remove units for all zero length values because these units aren't being used by the browser and therefore can be safely removed to save bytes.