var prevTab = 1;
 function showTab(tabName,tabX)
 {
  var oldTab = "tab_td_" + prevTab;
  document.getElementById(oldTab).className = '';
  oldTab = "tab_content_" + prevTab;
  document.getElementById(oldTab).style.display= 'none';
 
  prevTab = tabX;
  
  var newTab = "tab_td_" + prevTab;
  document.getElementById(newTab).className = 'main_tab';
  newTab = "tab_content_" + prevTab;
  document.getElementById(newTab).style.display= 'inline';
  document.getElementById(newTab).className = "tab_content";
 }