core/packages/template-explorer/style.css

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
}

#header {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 60px;
  box-sizing: border-box;
  background-color: #1e1e1e;
  border-bottom: 1px solid #333;
  padding: 0.3em 1.6em;
  color: #fff;
  z-index: 1;
}

h1 {
  font-size: 18px;
  display: inline-block;
  margin-right: 15px;
}

#options-wrapper {
  position: absolute;
  top: 20px;
  right: 10px;
}

#options-wrapper:hover #options {
  display: block;
}

#options-label {
  cursor: pointer;
  text-align: right;
  padding-right: 10px;
  font-weight: bold;
}

#options {
  display: none;
  margin-top: 15px;
  list-style-type: none;
  background-color: #1e1e1e;
  border: 1px solid #333;
  padding: 15px 30px;
}

#options li {
  margin: 8px 0;
}

#header a {
  font-weight: 600;
  color: rgb(101, 163, 221);
}

#header .label {
  font-weight: bold;
}

#header input {
  margin-right: 6px;
}

#header label {
  color: #999;
}

.editor {
  position: absolute;
  top: 60px;
  bottom: 0;
  box-sizing: border-box;
}

#source {
  left: 0;
  width: 45%;
}

#output {
  left: 45%;
  width: 55%;
}

.highlight {
  background-color: rgba(46, 120, 190, 0.5);
}