The css used in Java 7's Javadoc can be found here:

http://docs.oracle.com/javase/7/docs/api/stylesheet.css

You can then use the stylesheetfile attribute from the javadoc commandline, or ant or maven

from commandline:

%javadoc -stylesheetfile <path> ...

in ant:

<javadoc 
        ....
        stylesheetfile="/path/to/stylesheet.css"
        />      

in Maven (see Maven's stylesheet configuration page for more details ):

<reporting> (or <build>)
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-javadoc-plugin</artifactId>
        ...
        <configuration>
          <stylesheetfile>${basedir}/path/to/your/stylesheetfile.css</stylesheetfile>
          ...
        </configuration>
      </plugin>
    </plugins>
    ...
  </reporting> (or </build>) 

UPDATE

Stephen Colebourne has an article about other breaking changes to Javadoc in Java 8 here . Apparently, the doclint now enforces HTML 4 compliance and will not link if the link is broken or not 100% correct HTML 4. You can turn it off with -Xdoclint:none as an additional parameter.

<plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-javadoc-plugin</artifactId>
      <configuration>
        <additionalparam>-Xdoclint:none</additionalparam>
      </configuration>
    </plugin>
 </plugins>

Regarding the <code> tags in parameter descriptions, I did see that too. It looks like the parameter descriptions in javadoc are now always monospace so you don't need code tags anymore?