<pre> needs background-color and the syntax-highlighter checked

[Hb---]

Wiki text inside three curly brackets {{{is delivered as <code>if no line break</code> or as

<pre>when the brackets start the line.</pre>

This variant allows syntax-highlighting with Wiki Processors.

<code> is since #15910 well displayed within the limits of the Help Browser.

<pre> has two issues:

1. The formatting of the area lacks of a background-color (and a border, if possible). The area should look the same as in a normal web browser.
2. The result of the #!sh syntax-highlighter is wrong, i.e.
   • the line break after comment lines gets lost and
   • the colour for highlighted words gets lost too.

See the screenshot, especcially the orange coloured marks for missing line breaks: