Undesirable whitespace treatment in mail archive display

Since we moved to the new website design, the mailing list archives
display all messages with leading indentation suppressed.  This can
be pretty awful, eg in the code fragment here:

https://www.postgresql.org/message-id/20180611170812.7ypf6xs6dlteo57j@alap3.anarazel.de

Looking closer, I think it may not just be leading indentation that
gets lost; seems like *any* whitespace string gets smashed to a
single space, cf followup at

https://www.postgresql.org/message-id/7382.1528737252%40sss.pgh.pa.us

which certainly does not look like it did in my outbox.

I assume this is just an ill-considered stylesheet choice somewhere
... can we fix it please?

            regards, tom lane