100x100 pixel yellow box is positioned to top left relative
to the viewport. It should be on the top left corner
(position:fixed; top:0; left:0;).
The background image is positioned to top left relative to
the viewport and it should fit to the block box of the BODY element (background-attachment: fixed; background-position:
top left).
Red "measuring sticks" have yellow child blocks, which should be inside the red blocks at the same line. They should be floated left or right
(float:left and float:right).