I've started this with multiple aspect ratio support in mind.
And it was fine in 5:4, it was fine in 16:9, but it magically had a few pixels off here and there on the lower rows in 4:3/16:9.
Then I realized that the large keys (panels) had variations in size even by changing resolution under the same aspect ratio.
That's the disadvantage of working with fixed pixels/percentages (and quite possible, a bug in panorama css regarding alignment).
To obtain the proper result, I made one key on each row with:
width: fill-parent-flow( 1.0 );