Incorrect analysis when `font` contains `var()`

From github.com:

```
font:400 var(--primer-text-title-size-large, 2rem) -apple-system,BlinkMacSystemFont,"Segoe UI","Noto Sans",Helvetica,Arial,sans-serif,"Apple Color Emoji","Segoe UI Emoji"
```

reports `2rem` as a font-family

With many more similar examples.