Code blocks overflow their container.

Code blocks render without overflow control. Long lines of code render outside their containers.
A possible fix is for each user to add a custom CSS property.

```
pre{overflow-x: auto;}
```

This will add a horizontal scroll bar when the text overflows the container.
Perhaps this can be added to the default CSS files.

Locate the default CSS files that style rendered code blocks and inspect the rules for preformatted text. Add overflow control for long lines, then verify that code exceeding its container can scroll horizontally without affecting shorter blocks.

Written by the indexing model from the issue text.