doc-diff-improvements.css

/* Color values from RTD's Doc Diff addon's CSS */
.doc-diff-added   { --bgcolor: rgb(171, 242, 188) }
.doc-diff-removed { --bgcolor: rgba(255, 129, 130, 0.4) }

/* Doesn't work in Firefox 131… not sure why… *//*
.doc-diff-removed {
  --bgcolor: color(
    from rgba(255, 129, 130, 0.4)
    srgb
    calc(((1 - alpha) * 255) + (alpha * r))
    calc(((1 - alpha) * 255) + (alpha * g))
    calc(((1 - alpha) * 255) + (alpha * b))
    / 1
  )
}
*/

.doc-diff-removed {
  /* Hard code mixing rgba(255, 129, 130, 0.4) into white with no alpha. */
  --bgcolor: rgb(
    calc(((1 - 0.4) * 255) + (0.4 * 255))
    calc(((1 - 0.4) * 255) + (0.4 * 129))
    calc(((1 - 0.4) * 255) + (0.4 * 130))
  );
}

/* Add a 2px box "shadow" on all sides to mimic a 2px outline that sits
 * _behind_ other content instead of in front.
 */
.doc-diff-added, .doc-diff-removed {
  box-shadow:
    -2px -2px var(--bgcolor), /* NW */
     2px -2px var(--bgcolor), /* NE */
     2px  2px var(--bgcolor), /* SE */
    -2px  2px var(--bgcolor); /* SW */
}