CSS: hsl() & rgb() doesn't minify when inside of custom properties

[fqidz]

I'm not sure if it's intended, but this:

html {
    --color: hsl(0 17% 50%);
    --foo: rgb(1 2 3);
    background-color: hsl(0 2% 100%);
}

minifies to:

html{--color:hsl(0 17% 50%);--foo:rgb(1 2 3);background-color:#fff}

instead of:

html{--color:#956a6a;--foo:#010203;background-color:#fff}