gecko-dev/layout/generic/test/frame_selection_underline.css

html {
  font-size: 16px;
}

* {
  margin: 0;
  padding: 0;
}

@font-face {
  font-family: "AhemTest";
  src: url(../../../../tests/fonts/Ahem.ttf);
}

@font-face {
  font-family: "mplusTest";
  src: url(../../../../tests/fonts/mplus/mplus-1p-regular.ttf);
}

/* For aligning the two spacers (see below) to the left most and the right most,
   the div must create a new blocking format context. */
div#target {
  position: absolute;
}

span#decoration {
  margin-left: 0.333em;
}

body.reference div span#decoration {
  text-decoration: underline;
}

/* both ends of selection underlines for IME are clipped for making the
   boundaries of clauses in composition string clear.  These spacers will
   cover the ends in the reference. */
span#leftspacer, span#rightspacer {
  background-color: white;
  position: absolute;
  width: 1px;
  height: 100%;
  overflow: hidden;
}

span#leftspacer {
  left: 0.333em;
}

span#rightspacer {
  right: 0;
}