Remove wrong CSS font-color property (gatsbyjs#11047)

Fix CSS line-height property name

Remove unused longhand CSS padding properties

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## Description
This PR fixes a few CSS issues that were found during an analysis.

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## Related Issues

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  Link to the issue that is fixed by this PR (if there is one)
  e.g. Fixes gatsbyjs#1234, Addresses gatsbyjs#1234, Related to gatsbyjs#1234, etc.
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src/components/layout.css

@@ -398,10 +398,6 @@ pre {
   margin-left: 0;
   margin-right: 0;
   margin-top: 0;
-  padding-bottom: 0;
-  padding-left: 0;
-  padding-right: 0;
-  padding-top: 0;
   margin-bottom: 1.45rem;
   font-size: 0.85rem;
   line-height: 1.42;