message: Screen thumbnails UI refinements
  Add a little mouse hover highlight for the screen name
  (to give a hint that it's clickable)
  Center the plus sign vertically
diff: .tabs {
  display: flex;
  flex-direction: row;
  - align-items: center;
  + align-items: flex-start;
  }
  .tab {
  }
  .tab.newScreen {
  + /* margin-top/bottom + padding is for vertically centering the
  + plus sign. */
  + margin-top: auto;
  + margin-bottom: auto;
  + padding-bottom: 18px;
  padding-left: 20px;
  padding-right: 20px;
  color: rgb(173,173,173);
  .tabName {
  font-size: 12px;
  - width:100%;
  + width:97%;
  height: 14px;
  - padding-top: 5px;
  + margin-top: 6px;
  + padding-left: 2px;
  + padding-right: 2px;
  color: rgb(120, 120, 120);
  + outline: solid;
  + outline-width: 1px;
  + outline-color: rgba(255,0,0,0);
  +}
  +
  +.tabName:hover {
  + outline: solid;
  + outline-width: 1px;
  + outline-color: rgba(64,64,64,255);
  }
  .tabNameEditor {
  font-size: 12px;
  width: 100%;
  height: 14px;
  - padding-top: 5px;
  + margin-top: 5px;
  color: rgb(120, 120, 120);
  }
  width: 100%;
  box-sizing: border-box;
  background-color: #333;
  - border-color: #222;
  color: rgb(170,170,170);
  border-style: none;
  padding: 0px;
  