Error Length value missing a unit

Example

/* Wrong: no unit */
.box { margin: 10; padding: 5; }

/* Right */
.box { margin: 10px; padding: 0.5rem; }

/* Fine: zero never needs a unit */
.box { border-width: 0; }

Why it matters

CSS length values require a unit for any non-zero number — this is one of the few places the spec makes zero a genuine special case, since a length of zero is the same regardless of unit. A bare number like 10 on a property like margin is not valid CSS, and the browser drops the entire declaration rather than guessing which unit you meant. This is a common mistake coming from JavaScript or other languages where a numeric style value is often set without a unit — many DOM APIs and CSS-in-JS libraries add px automatically, which can make the omission feel natural in a way it isn't in plain CSS.