Tests for `font-weight: 1000;`

According to the CSS spec:

"values greater than or equal to 1 and less than or equal to 1000 are valid" source

However, this is not yet fully supported in Firefox or Safari.

A simple test

The left column (red) uses font-weight: 1000;.

The right column (blue) uses font-variation-settings: 'wght' 1000;.

The middle column should perfectly overlap (it will look purple if it does). If it doesn't, font-weight: 1000; doesn't work.

In Firefox 70 on macOS: font-weight values above 900 is ignored and falls back to 900.
In Safari on macOS: font-weight values up to 999 work, but font-weight: 1000; is marked as invalid and weight falls back to 400)
In Chrome 78 on macOS, this test works as intended.