How keep table header positions fixed with vertical scroll and horizontal scroll in a html page

How keep table header positions fixed with vertical scroll and horizontal scroll in a html page

How could keep the table headr position fixed, when I scroll the html with horizontal or vertical scroll? Thanks a lot.

Example Page: http://para.maximintegrated.com/en/search.mvp?fam=stepdn&270=Internal%20Pwr.%20FETs&tree=powersupplies

My Failed Case