RFR: 8332239: Improve CSS for block tags

[Hannes Wallnöfer]

Please review a change to improve the layout of definition lists used to display block tags:

 - Add indentation to the `<dd>` elements used for block tag details
 - Set the margin of lists within block tag details so they do not appear as nested lists, except for lists with CSS classes `tag-list` or `tag-list-long`, which are used for block tags containing lists, such as `@see`. 

Before/after comparison (contains `java.base` and `java.compiler` modules):
https://cr.openjdk.org/~hannesw/8332239/api.00/index.html
https://cr.openjdk.org/~hannesw/8332239/api.01/index.html

Comparison for block tag layout:
https://cr.openjdk.org/~hannesw/8332239/api.00/java.base/java/lang/Object.html#hashCode()
https://cr.openjdk.org/~hannesw/8332239/api.01/java.base/java/lang/Object.html#hashCode()

Example of very long block tag details containing a list:
https://cr.openjdk.org/~hannesw/8332239/api.00/java.compiler/javax/lang/model/util/package-summary.html
https://cr.openjdk.org/~hannesw/8332239/api.01/java.compiler/javax/lang/model/util/package-summary.html

Note that the indentation also applies to the definition lists at the top of class/interface documentation as they use the same markup as block tags. This was not an intended change, but is hard to avoid without deeper changes to the markup or CSS:
https://cr.openjdk.org/~hannesw/8332239/api.00/java.base/java/lang/Exception.html
https://cr.openjdk.org/~hannesw/8332239/api.01/java.base/java/lang/Exception.html

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Commit messages:
 - JDK-8332239: Improve CSS for block tags

Changes: https://git.openjdk.org/jdk/pull/19264/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19264&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332239
  Stats: 8 lines in 1 file changed: 5 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/19264.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19264/head:pull/19264

PR: https://git.openjdk.org/jdk/pull/19264