Skip to main content

HTML Guide

Free site validation

Find out what web pages on your sites are affected by HTML issues.

CSS: “mask”: Too many values or values are not recognized.

The specified CSS mask has incorrect or unrecognized values. Ensure that the mask property is used correctly according to the CSS specifications.

The mask CSS shorthand property hides an element (partially or fully) by masking or clipping the image at specific points.

For example, the mask-image CSS property sets the image that is used as mask layer for an element. By default this means the alpha channel of the mask image will be multiplied with the alpha channel of the element, as in thie example:

<!DOCTYPE html>
<html lang="en">
  .masked {
    width: 100px;
    height: 100px;
    background-color: #8cffb0;
    -webkit-mask-image: url(sun.svg);
    mask-image: url(sun.svg);
  <div class="masked"></div>

Learn more:

Related W3C validator issues