This is how Bootstrap’s grid system works - Bootstrap uses span elements to establish a grid, and puts a margin on the left of each span to put space between each column of the grid — so naturally if you have rows on that grid, they’d be offset by 12px — so the -12px resets that…
I’d wager to guess that the topic page isn’t set up to follow the grid 100%, hence the noticeable offset. For now removing that -12px from Bootstrap’s CSS would mess up the alignment of other pages (the topic page, for example) and things would be off for everyone, not just those on the topic page on narrow screens…
Anyway, for now I just added a 12px margin to the posts wrapper to compensate, that should probably fix it (I might undo it if it affects anything else though)…
