'Javascript Selector' for CSS

Sometimes you want to selectively display certain elements on a webpage depending on whether or not the user has Javascript enabled. Here's a neat trick to do so!

Add the no-js class to the html element:
```
<html class="no-js">
  ...
</html>
```

Load the following Javascript code:

document.documentElement.classList.remove("no-js");
document.documentElement.classList.remove("js");

Include the following CSS:

:root.no-js .when-js {
  display: none !important;
}

:root.js .when-no-js {
  display: none !important;
}

Now you can add the when-js/when-no-js class to elements to only show it when Javascript is enabled/disabled!