Another CSS alternative exists (an alternative using CSS to address this horizontal-scrolling problem).

davido offered:

duplicate perl environments uses <pre> tags, which are a longstanding problem, not just in PerlMonks, but just about everywhere. If it's a big problem you could specify in your CSS that pre blocks should be constrained to a maximum size, and should be scrollable.

How-dy! It ought to noted that few formatting mishaps on Perlmonks are as irritating to me (and considerable other users) as long-line posts (horiz. scrolling). The <pre> tag is indeed deprecated at Perlmonks, but is it a reasonable expectation that most users without long experience here will remember that? Plus, is it (apparently) true that users diligently check the markup they are using against the Monastery guidelines? Point taken perhaps without me going on and on about user behavior ...

A code solution always seems attractive when one can be found. Here's one for the PRE problem on Perlmonks nodes:

  /* style frag CSS */
 pre { white-space : pre-wrap }
[download]

The pre-wrap is defined at w3.org as doing:

This value prevents user agents from collapsing sequences of white space. Lines are broken at newlines in the source, at occurrences of "\A" in generated content, and as necessary to fill line boxes.

and is from the CSS Level 2 spec.

I am not on the inside wrt nuts and bolts of the Everything machine and the production of markup on PMo. So I have to leave it to someone else to work out the best way to actually implement the application of a default style setting (that is different from the default in most user agents). But a simple approach would be to just change the Common CSS for all Themes.