After using a Javadoc documentation directory built by JDK 1.3.1 in a Mozilla dev build, I noticed that it was printing some warnings to console about parsing the stylesheet, specifically problems with parsing font-size. I traced them back to some suspicious lines in j2se/src/share/classes/com/sun/tools/doclets/standard/StylesheetWriter.java (I have 1.4.0 sources):

println(".FrameTitleFont   { font-size: 10pts; font-family: Helvetica, Arial, san-serif }");
println(".FrameHeadingFont { font-size: 10pts; font-family: Helvetica, Arial, san-serif }");
println(".FrameItemFont    { font-size: 10pts; font-family: Helvetica, Arial, san-serif }");

1. Probably should s/10pts/10pt/g

2. and s/san-serif/sans-serif/g

I am not sure how best to confirm that a CSS stylesheet is valid and functioning correctly, but this does *appear* to be a bug. Note that the commented-out example line looks better:

print("/* "); 
print(".FrameItemFont  { font-size: 10pt; font-family: ");
print("Helvetica, Arial, sans-serif }"); println(" */");

Hopefully someone more knowledgeable can take this as a cue to check the standard stylesheet for these and other errors.
  xxxxx@xxxxx   2003- customer -28

N/A

This has been fixed in 1.4.2 (mantis) as bug 
4417174:  Creates invalid stylesheet.css file (font-size: normal)
Closing as a duplicate.
  xxxxx@xxxxx   2003-02-28