Change the selected avatar image box to green?

Not a big issue, but in terms of GUIs in general, red is supposed to signal "Danger, stay away!". So perhaps it's worth considering changing the "this is the avatar you selected" box colour from red to green?

In avatar_selection.css, line 21, new version suggested:

body div.user-avatar-select label.option img.avatar-select {
  border: 4px #00FF00 solid;
  padding: 1px;
}