Fix CSS with @media print to hide header when printing

If you print the document from the browser, the header shows up. I would expect it to be hidden. Additionally, the main content should have no padding –on print– to make a better use of the page size.

This could be a solution:

```css
@media print {
#page-header {
display: none;
}
.markdown-body {
padding: 0;
}
}
```

Or is this intentional? If that is the case, maybe the user should be able to toggle the header (like the dark mode), to be able to print with or without it.