hedgedoc/public/css/slide-preview.css

.markdown-body.slides {
  position: relative;
  z-index: 1;
  color: #222;
}

.markdown-body.slides::before {
  content: '';
  display: block;
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  z-index: -1;
  background-color: currentColor;
  box-shadow: 0 0 0 50vw;
}

.markdown-body.slides section[data-markdown] {
  position: relative;
  margin-bottom: 1.5em;
  background-color: #fff;
  text-align: center;
}

.markdown-body.slides section[data-markdown]::before {
  content: '';
  display: block;
  padding-bottom: 56.23%;
}

.markdown-body.slides section[data-markdown] div:first-child {
  position: absolute;
  top: 50%;
  left: 1em;
  right: 1em;
  transform: translateY(-50%);
  max-height: 100%;
  overflow: hidden;
}

.markdown-body.slides section[data-markdown] ul {
  display: inline-block;
}

.markdown-body.slides > section > section + section::after {
  content: '';
  position: absolute;
  top: -1.5em;
  right: 1em;
  height: 1.5em;
  border: 3px solid #777;
}