sign()

The sign() CSS function contains one calculation, and returns -1 if the numeric value of the argument is negative, +1 if the numeric value of the argument is positive, 0⁺ if the numeric value of the argument is 0⁺, and 0⁻ if the numeric value of the argument is 0⁻.

/* property: sign(expression) */
top: sign( --value );

The sign() function takes only one expression as its argument.

For example, in background-position positive percentages resolve to a negative length, and vice versa, if the background image is larger than the background area. Thus sign(10%) might return 1 or -1, depending on how the percentage is resolved! (Or even 0, if it's resolved against a zero length.)

div {
  background-position: sign(10%);
}

Another usecase is to control the position of the element. Either a positive or a negative value.

div {
  position: absolute;
  top: calc( 100px * sign( var( --value ) ) );
}

• abs()