Docs/CSS: Amend code block rendering.

This commit aims to improve the rendering of code blocks by
reducing the padding, matching the font-size with the rest of the
documentation text and finally, by changing the background colour
back to white from its current gray-ish state which matches the
background colour and making it really hard to spot the code.

Note: The BG colouring issue is due to converting the main BG
to gray whilst missing to change parts that where gray to white, i.e.,
not making the complete switch.

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)

docs/theme/mkdocs/css/base.css

@@ -55,10 +55,10 @@ h6,
   margin-bottom: 1.2em;
 }
 #content pre {
-  margin: 2em 0em;
-  padding: 1em 2em !important;
+  margin: 1em 0em;
+  padding: 0.5em 0.75em !important;
   line-height: 1.8em;
-  font-size: 1em;
+  background: #fff;
 }
 #content blockquote {
   background: #f2f2f2;