CSS Regions: separate floats with percent size in sized region

Test passes if you see some filler gray text and three blue squares inside a black-bordered rectangle. One blue square should be in the top left corner, another in the top right corner and the third one should be somewhere along the left border, below the top-left one.
Test fails is you see any red.

This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is

filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text. This is filler text.