framework/extensions/markdown/less/common.less

.MarkdownToolbar {
  display: inline-block;
}

span.spoiler {
  // Style the inline spoiler itself: a dark block, invisible font
  background: #444;
  color: transparent;

  // Try to generically hide all possible children
  * {
    // Links and other interactive elements would give their presence
    // away when hovering
    pointer-events: none;

    // Children can have special text or background colors
    background: transparent;
    color: transparent;
  }

  // Hide images visually
  img {
    visibility: hidden;
  }
}