tag-styles.css in Extensible BBCode 4.0.x

/* Remove some of the unrestricted form element style. */
label.xbbcode-spoiler {
  display: inline;
  font-weight: inherit;
  line-height: unset;
}

/* Hide the checkbox. */
input.xbbcode-spoiler {
  display: none;
}

/* Protect the label, as well as its children. This is needed because
 * the label is inline and its box may not fully cover its children.
 */
input.xbbcode-spoiler:not(:checked) + label.xbbcode-spoiler,
input.xbbcode-spoiler:not(:checked) + label.xbbcode-spoiler * {
  color: black;
  background: black;
}