code: function(w, h) {
      grids[0].set( space.size.$multiply( 0.1 ) ).to( space.size.$multiply( 0.9, 0.3 ) ).init( 50, 50, "fix", "fix" );
      grids[1].set( space.size.$multiply( 0.1, 0.4 ) ).to( space.size.$multiply( 0.9, 0.6 ) ).init( 50, 50, "flex", "flex" );
      grids[2].set( space.size.$multiply( 0.1, 0.7 ) ).to( space.size.$multiply( 0.9, 0.9 ) ).init( 5, 8, "stretch", "stretch" );
    }
docs: callback to reset grid when space is resized