gecko-dev/testing/mochitest/static/harness.css

body   {
  margin: 0;
  padding: 0;
  font-family: Verdana, Helvetica, Arial, sans-serif;
  font-size: 11px;
  background-color: #fff;
}

#xulharness {
  position: fixed; 
  top: 30px;
  bottom: 0;
  right: 0px;
  left: 0px;
  overflow:auto;
}

th, td {
  font-family: Verdana, Helvetica, Arial, sans-serif;
  font-size: 11px;
  padding-left: .2em;
  padding-right: .2em;
  text-align: left;
  height: 15px;
  margin: 0;
}

li, li.test, li.dir {
  padding: 0;
  line-height: 15px;
}

ul { 
  list-style: none;
  margin: 0;
  margin-left: 1em;
  padding: 0;
  border: none;
}

ul.top { 
  padding: 0;
  padding-left: 1em;
}

table#test-table {
  background: #f6f6f6;
  margin-left: 1em;
  padding: 0;
}

div.container {
  margin: 1em;
}

a#runtests, a {
  color: #3333cc;
}

li.non-test a { 
  color: #999999;
}

small a {
  color: #000;
}

.clear { clear: both;}
.invisible { display: none;}

div.status {
  min-height: 170px;
  width: 100%;
  border: 1px solid #666;
}
div.frameholder {
  min-height: 170px;
  min-width: 500px;
  background-color: #ffffff;
}

div#current-test {
  margin-top: 1em;
  margin-bottom: 1em;
}

#indicator {
  color: white;
  background-color: green;
  padding: .5em;
  margin: 0;
}

#pass, #fail {
  margin: 0;
  padding: .5em;
}

#testframe {
  width: 500px;
  height: 300px;
}


body[singletest=true] table,
body[singletest=true] h2,
body[singletest=true] p,
body[singletest=true] br,
body[singletest=true] .clear,
body[singletest=true] .toggle,
body[singletest=true] #current-test,
body[singletest=true] .status {
  display: none;
}


body[singletest=true],
body[singletest=true] .container,
body[singletest=true] .frameholder,
body[singletest=true] #testframe {
  display: flex;
  flex: 1 1 auto;
  height: 100%;
  box-sizing: border-box;
  margin: 0;
}