<dd> elements in <dl> lists look terrible, because they are displayed in monotype. E.g. look at

http://download.java.net/jdk9/docs/api/java/util/concurrent/ThreadPoolExecutor.html

after "Core and maximum pool sizes"

Looking at src/jdk.javadoc/share/classes/com/sun/tools/doclets/internal/toolkit/resources/stylesheet.css
that seems to be intentional, but I can't see any reason for it.
I tried the obvious change

--- a/src/jdk.javadoc/share/classes/com/sun/tools/doclets/internal/toolkit/resources/stylesheet.css
+++ b/src/jdk.javadoc/share/classes/com/sun/tools/doclets/internal/toolkit/resources/stylesheet.css
@@ -304,7 +304,6 @@
 .contentContainer .description dl dd, .contentContainer .details dl dd, .serializedFormContainer dl dd {
     margin:5px 0 10px 0px;
     font-size:14px;
- font-family:'DejaVu Sans Mono',monospace;
 }
 .serializedFormContainer dl.nameValue dt {
     margin-left:1px;

and that greatly improved the generated javadoc appearance.

Consider getting a real CSS expert to review stylesheet.css