line-highlight.css

.reveal
  div.sourceCode
  pre
  code.has-line-highlights
  > span:not(.highlight-line) {
  opacity: 0.4;
}

.reveal pre.numberSource {
  padding-left: 0;
}

.reveal pre.numberSource code > span {
  left: -2.1em;
}

pre.numberSource code > span > a:first-child::before {
  left: -0.7em;
}

.reveal pre > code:not(:first-child).fragment {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  box-sizing: border-box;
}

.reveal div.sourceCode pre code {
  min-height: 100%;
}