css/css-pseudo/first-line-allowed-properties.html

<!DOCTYPE html>
<title>CSS Test: Properties allowed on ::first-line pseudo elements</title>
<link rel="help" href="https://drafts.csswg.org/css-pseudo-4/#first-line-styling">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
  #target::first-line {}
  #target { visibility: hidden; }
</style>
<div id="target">text</div>
<script>
  let style;
  const target = document.querySelector("#target");
  const defaultComputedStyle = getComputedStyle(target);

  test(() => {
    var styleRule = document.styleSheets[0].cssRules[0];
    assert_equals(styleRule.selectorText, "#target::first-line", "make sure we have the correct style rule");
    style = styleRule.style;
  }, "retrieve style rule");

  const validProperties = {
    backgroundAttachment: "fixed",
    backgroundBlendMode: "hue",
    backgroundClip: "padding-box",
    backgroundColor: "rgb(10, 20, 30)",
    backgroundImage: "linear-gradient(rgb(0, 0, 0), rgb(255, 255, 255))",
    backgroundOrigin: "border-box",
    backgroundPosition: "50% 50%",
    backgroundRepeat: "no-repeat",
    backgroundSize: "10px 20px",
    color: "rgba(10, 20, 30, 0.4)",
    fontFamily: "sans-serif",
    fontFeatureSettings: '"vert" 2',
    fontKerning: "none",
    fontSize: "30px",
    fontSizeAdjust: "0.5",
    fontStyle: "italic",
    fontVariant: "small-caps",
    fontWeight: "900",
    fontVariationSettings: '"XHGT" 0.7',
    letterSpacing: "12px",
    opacity: "0.5",
    textDecoration: "overline wavy rgb(10, 20, 30)",
    textJustify: "none",
    textShadow: "rgb(10, 20, 30) 10px 20px 30px",
    textTransform: "capitalize",
    textUnderlinePosition: "under",
    verticalAlign: "12%",
    wordSpacing: "12px"
  };

  const invalidProperties = {
    border: "40px dotted rgb(10, 20, 30)",
    borderImage: "linear-gradient(rgb(0, 0, 0), rgb(255, 255, 255)) 10% / 20 / 30px repeat",
    borderRadius: "10px 20px",
    margin: "10px 20px 30px 40px",
    padding: "10px 20px 30px 40px",
    position: "absolute",
    transition: "transform 1s",
    transform: "rotate(45deg)",
    wordBreak: "break-all"
  };

  function testFirstLineProperty(property, rule, expected, reason) {
    test(function() {
      style[property] = "";
      style[property] = rule;
      assert_equals(getComputedStyle(target, "::first-line")[property], expected);
      style[property] = "";
    }, reason);
  }

  for (let property in validProperties) {
    testFirstLineProperty(property, validProperties[property], validProperties[property],
                            property + " should be applied to first-line pseudo elements.");
  }

  for (let property in invalidProperties) {
    testFirstLineProperty(property, invalidProperties[property], defaultComputedStyle[property],
                            property + " should not be applied to first-line pseudo elements.");
  }
</script>