In all current CSS properties, percentages are resolved against some other concrete type, so we defined calc() such that percentages always "resolve away" and don't show up in the final value.
But in Houdini APIs, a custom property might just accept a percentage by itself, and that's reasonable. (If we were remaking CSS today, we'd probably do that for 'opacity' - it's silly that it allows a number too.) So, calc() should allow "percentage" to be a resolved type.
Originally from w3c/css-houdini-drafts#249
In all current CSS properties, percentages are resolved against some other concrete type, so we defined calc() such that percentages always "resolve away" and don't show up in the final value.
But in Houdini APIs, a custom property might just accept a percentage by itself, and that's reasonable. (If we were remaking CSS today, we'd probably do that for 'opacity' - it's silly that it allows a number too.) So, calc() should allow "percentage" to be a resolved type.
Originally from w3c/css-houdini-drafts#249