[devote]

function setCSS () {
   var i, str1 = document.getElementsByTagName("Stroka1"),
        str2 = document.getElementsByTagName("Stroka2");

   for( i = 0; str1[i]; i++ ) {
      str1[ i ].style.backgroundColor = str1[ i ].style.backgroundColor == "#ffffff" ? "#c0c0c0" : "#ffffff";
   }
   for( i = 0; str2[i]; i++ ) {
      str2[ i ].style.backgroundColor = str2[ i ].style.backgroundColor == "#ffffff" ? "#c0c0c0" : "#ffffff";
   }
}