'property: 0' or 'property: 0px' in CSS?
Solution 1:
Unit identifiers are optional, but there is no noted performance increase (although you are saving two characters).
CSS2 - From W3C CSS 2.1 Specification for Syntax and basic data types:
The format of a length value (denoted by <length> in this specification) is a <number> (with or without a decimal point) immediately followed by a unit identifier (e.g., px, em, etc.). After a zero length, the unit identifier is optional.
(Emphasis mine)
CSS3 - From W3C CSS Values and Units Module Level 3 (Currently in Candidate Recommendation at the time of this writing)
For zero lengths the unit identifier is optional (i.e. can be syntactically represented as the 0).
Solution 2:
While the unit is optional when the value is 0
, I tend to leave it in, as I can then tweak the values with Chrome's Developer Tools by clicking on the value and pressing the up/down arrow keys. Without a unit, that isn't really possible.
Also, CSS minifiers strip the units off of 0
values anyways, so it won't really matter in the end.