dart/editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/generator/project/app.css

body {
  background-color: #F8F8F8;
  font-family: 'Open Sans', sans-serif;
  font-size: 14px;
  font-weight: normal;
  line-height: 1.2em;
  margin: 15px;
}