Add styling to controls so they stack nicely

Remove styling for bare `button`, require `.button` on buttons

Only show last part of URL under progress bar, if a URL is playing

Give the `die()` link a button styling, as it performs the action without
confirmation
rm !opacity from history, replace with small text

* rm opacity from history, as it made buttons look odd (and felt like cheating)
* add styles for footer links
* add strikethrough to language selection