.logged-in .CodeMirror:before,
 body.logged-in:before {
 content: "Warning: Grading is taking place. Making changes at this point will result in test failure. All changes made during this period will be lost.";
 text-align: center;
 background: yellow;
 color: black;
 display: block;
 padding: 20px;
 z-index: 10000000000000000;
  position: fixed;
  bottom: 0px;
  right: 0px;
  left: 0px;
  border-top: 3px solid black;
}

.logged-in .CodeMirror:before,
body.logged-in:after {
 content: "Warning: Grading is taking place. Making changes at this point will result in test failure. All changes made during this period will be lost.";
 text-align: center;
 background: yellow;
 color: black;
 display: block;
 padding: 20px;
 z-index: 10000000000000000;
 border-top: 23px solid black;
}