The var() function doesn't work as part of border shorthand property

[ham2anv]

Not sure if this applies to other properties, but I ran into this today in the border shorthand property. The following:

border: 0.15rem solid var(--highlight, black);

throws the error "WARNING: Ignored border: 0.15rem solid var(--highlight, black) at 8:5, invalid value.". Breaking the var() out into its own border-color property fixes the issue.

[mikevoets]

The same seems to happen when concatenating var with other text:

E.g. where --table-label: 'Table', the following declaration:

content: 'var(--table-label) ' 1. ';

results in "Table", and not "Table 1. "

[mikevoets]

The bug described in my comment is unrelated to the OP.

@ham2anv @liZe the issue here is that a variable token is yet undetermined at weasyprint/css/validation/expanders.py:241 so it will raise InvalidValues. It is unknown what kind of declaration a variable is at this point.

[liZe]

Now covered by #1219.