Disallow units for zero lengths.
a { top: 0px; }
/** ↑↑
* This zero and this type of length unit */Lengths refer to distance measurements. A length is a dimension, which is a number immediately followed by a unit identifier. However, for zero lengths the unit identifier is optional. The length units are: em, ex, ch, vw, vh, cm, mm, in, pt, pc, px, rem, vmin, and vmax.
The following patterns are considered warnings:
a { top: 0px }a { top: 0.000em }The following patterns are not considered warnings:
a { top: 0 } /* no unit */a { transition-delay: 0s; } /* dimension */a { top: 2in; }a { top: 1.001vh }