Increase drawer width for Explain This Vulnerability feature

The drawer that shows the explanation for the Explain This Vulnerability feature is 400px wide, but when there's a code sample, it's too narrow and requires horizontal scrolling to see all of the code:

We should expand the drawer width so that it will show at least 80 characters of code before requiring horizontal scrolling. The drawer also needs to stay responsive when the width is below 768px, where it expands to the full page width.