[jfx11u] RFR: 8204568: Relative CSS-Attributes don't work all time

[Ambarish Rapte]

Backport had a minor merge conflict of copyright year in the file `Labeled.java`.
Rest of the changes are clean backport

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Commit messages:
 - 8204568: Relative CSS-Attributes don't work all time

Changes: https://git.openjdk.java.net/jfx11u/pull/6/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=6&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8204568
  Stats: 700 lines in 5 files changed: 696 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/6.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/6/head:pull/6

PR: https://git.openjdk.java.net/jfx11u/pull/6