position: absolute;
          left: 20px;
          top: 20px;
        

The only containing element for this div is the main window, so it positions itself in relation to it.

          position: relative;
          top: 0;
          right: 0;
        

Relative positions itself in relation to its siblings.

          float: right;
          position: relative;
          top: 20px;
          left: 20px;
        

Relative to its sibling div above, but removed from flow of content.

            position: absolute;
            top: 10px;
            left: 20px;