CSS calc-size() function

[dbaron]

WebKittens

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Title of the spec

CSS calc-size() function

URL to the spec

https://drafts.csswg.org/css-values-5/#calc-size

URL to the spec's repository

https://github.com/w3c/csswg-drafts/issues

Issue Tracker URL

No response

Explainer URL

https://github.com/w3c/csswg-drafts/blob/main/css-values-5/calc-size-explainer.md

TAG Design Review URL

w3ctag/design-reviews#955

Mozilla standards-positions issue URL

mozilla/standards-positions#1022

WebKit Bugzilla URL

https://bugs.webkit.org/show_bug.cgi?id=274177

Radar URL

No response

Description

Animation to or from auto heights is commonly requested by web developers. It is important for animation of elements (such as the contents of disclosure widgets) opening/closing between a content-based height (or width) and a small (often zero) height (or width). This calc-size() proposal fits the desire to do such animations into the way that CSS transitions and animations work. More generally, this allows animating between a fixed length and almost any type of height (or width, or min/max-height/width) that can currently be specified in CSS.

The CSS calc-size() function is a CSS function similar to calc(), but that also supports operations on exactly one of the values auto, min-content, max-content, fit-content, stretch, or contain, which are the intrinsic sizing keywords. This allows transitions and animations to and from these values (or mathematical functions of these values), as long as the calc-size() function is used on at least one of the endpoints of the transition or animation to opt in.