Border pixel snapping

View at 100% zoom. Every box sits at a fractional position (the 15mm page margin is 56.69px itself), so a 1px border either covers one device column (snapped) or two half-covered ones (exact).

1px borders at different fractional offsets

Cards in a row (the original report)

Horizontal rules (border-top: 1px)

Border on a background

The background is snapped with the border, so no background shows outside it.

Border with an outline

The outline follows the snapped border.

Other border styles, 2px

Table cells (separate borders)

Table cells (collapsed borders, with backgrounds)