cqb

1cqb is 1% of the container’s block size: the height in horizontal text and the width in vertical text. Like cqh, it needs a container whose block size does not depend on its children, which means container-type: size.

In a container that only has inline-size containment, cqb looks for another ancestor that does measure the block axis, and uses the small viewport block size when there is none. With no such ancestor, ten cqb inside it equals ten svb, and since a card normally has no say in how tall the window is, the number is usually not what the author intended. With an outer container-type: size box 300px tall around it, ten cqb was 30px, taken from the outer box while cqi on the same element came from the inner one.

As with cqi, the axis is the one of the element using the unit. In Chromium, an element set in vertical-rl inside a horizontal container read its cqb along the container’s width, because for that element the block direction runs sideways. Choose cqb over cqh for the same reason you choose cqi over cqw: it follows the writing mode, where cqh always means the physical height.