Vimium Black Monospace theme.

VimiumTheme.css

/*
  Installation:
    1. Right Click on the Vimium icon
    2. Select "Options"
    3. On the footer, click on "Show Advanced Options"
    4. Paste this inside "CSS for link hints" textbox
    5. On the footer, click on "Save Changes"
*/
div > .vimiumHintMarker {
  background: #000;
  border: 0;
  border-radius: 0px;
  box-shadow: RGBA(0, 0, 0, .5) 0 2px 10px;
  padding: 4px;
}

div > .vimiumHintMarker span {
  color: #FFF;
  font-family: monospace;
  font-size: 11px;
  font-weight: 100; 
  margin: 0 2px;
  text-shadow: none;
}

div > .vimiumHintMarker > .matchingCharacter {
  color: #999;
}