Tap to drop each block. Line it up perfectly to keep your width — miss and the tower gets thinner.
A block slides back and forth above your tower. Tap, click, or press Space to drop it onto the block below. Only the overlapping part sticks — anything hanging over the edge falls away, so the tower gets narrower with every imperfect drop. Miss completely with no overlap at all, and the run ends.
Drop a block close enough to a perfect line-up and it snaps to the exact width of the one below instead of shrinking, and builds a combo streak worth bonus points. The tower speeds up the higher you go, so a long perfect streak becomes harder to keep alive the further you push it.