Missing media attribute for the meta tag

The "media" attribute is not available for meta tags, so something like this is currently impossible:

```
<meta name="theme-color" 
      content="#ecd96f" 
      media="(prefers-color-scheme: light)">
<meta name="theme-color" 
      content="#0b3e05" 
      media="(prefers-color-scheme: dark)">
```

Would you want me to create a PR?