Bug 212522

CSS clamp() function is missing two features that the rest of the browsers have implemented:


First, it does not allow for calculating the font size:

```html
  <h2>Clamp Me</h2>

  <style>
    h2 {
      font-size: clamp(30px, 20vw + 5rem, 300px);
      /* Or with calc(), which isn't needed: */
      font-size: clamp(30px, calc(20vw + 5rem), 300px);
    }
  </style>
```

This feature is needed because viewport units as font sizes are inaccessible as they do not get bigger/smaller when the user zooms in or out. 


Second, the browser doesn't repaint the size of the font when the browser is resized:

```html
  <h2>Clamp Me</h2>

  <style>
    h2 {
      font-size: clamp(30px, 20vw, 300px);
    }
  </style>
```


Resize the browser, and you'll see the font size doesn't change. Reload the page at a smaller browser width and it does resize. 


Confirmed in Release 107 (Safari 13.2, WebKit 15610.1.14.1)