In CSS box alignment the alignment subject is the thing (or things) being aligned within the by the property.

For and , the alignment subject is the margin box of the box the property is set on, using the writing mode of that box. For and , the writing mode of the box is also used.

The definition of the alignment subject depends on the layout mode being used.

• Block containers (including table cells)

  • : The entire content of the block as a single unit.

  Multicol containers

  • : The column boxes, with any spacing inserted between column boxes added to the relevant column gaps.

  Flex containers

  • : For , the flex items in each flex line. For , the flex lines. Note, this only has an effect on multi-line flex containers.

  Grid containers

  • : The grid tracks in the appropriate axis, with any spacing inserted between tracks added to the relevant gutters. Collapsed gutters are treated as a single opportunity for space insertion.

See also

• CSS box alignment module

Related glossary terms: