minor #13495 [FrameworkBundle] Keep "pre" meaning for var_dump quick-and-dirty debug (giosh94mhz)

This PR was merged into the 2.3 branch.

Discussion
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[FrameworkBundle] Keep "pre" meaning for var_dump quick-and-dirty debug

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

This is a minor fix to have a quick-and-dirty var_dump nicely work with the exception output from Symfony.
In short, the default "pre" whitespace CSS rules should be kept outside of block "#content", so that var_dump output is not diplayed in a single huge line.

Commits
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b6d4390 Keep "pre" meaning for var_dump quick-and-dirty debug

Author: fabpot

Resources/public/css/structure.css

@@ -62,7 +62,7 @@ img {
     width: 970px;
     margin: 0 auto;
 }
-pre {
+#content pre {
     white-space: normal;
     font-family: Arial, Helvetica, sans-serif;
 }