We didn't get nuts with the style sheet but what I did was change the persistent menu links via the LPL for "LCMEmployeeMenu" (via the customization console in landmark).
As far as their stock look (all white, some grey) we just went with it, though that can be changed via the CSS in the site directory : /ENV/src/ltm/modules/hr/webapps/EmployeeSelfService/src
I did add the S3 links for payroll data (pay checks, direct deposit, payment calculator, withholdings).
Only problem was when clicked, the entire page was replaced with the S3 link, losing the persistent menu, logout, etc.
To get everything under the menu, I added some javascript to the welcome.html page that parses url parameters and pass what page I want to go to, then replace the innerHTML of the class 'inforScrollableArea' with an iframe that loads the S3 page (the iframe gets you a scroll bar in the sub content). Then the actual link is a link to the HTML5 EMSS with the appropriate parameter.
To make it all "live" you redeploy it via : enterprise app
hcmapp