gtk2/testsuite/css/parser/border-image-source.css

a {
  border-image-source: initial;
}

b {
  border-image-source: inherit;
}

c {
  border-image-source: unset;
}

d {
  border-image-source: none;
}

e {
  border-image-source: linear-gradient(yellow, blue);
}