window.onload = function() {
  // TAB1 - 가로 탭 1
	for(var i=1; i<=3; i++){
	  var tab1_head = document.getElementById("tab1_head"+i);
		tab1_head.style.position = "absolute";

    var tab1_link = document.getElementById("tab1_link"+i);

    if ( i == 1){
      tab1_link.onclick = function () {showhide(1, 0, 0); return false;}
    } else if ( i == 2 ) {
      tab1_link.onclick = function () {showhide(0, 1, 0); return false;}
    } else if ( i == 3 ) {
      tab1_link.onclick = function () {showhide(0, 0, 1); return false;}
    } 
  }

  showhide(1, 0, 0);  

}
  
function showhide() {
  for (var i=0; i<3; i++) {
    var tab1_list = document.getElementById("tab1_list"+(i+1));
    var tab1_btn = document.getElementById("tab1_btn"+(i+1));
    if ( arguments[i] == 1 ){
      tab1_list.style.display = "block";
      tab1_btn.src = tab1_btn.src.replace("_off", "_on");
    } else {
      tab1_list.style.display = "none";
      tab1_btn.src = tab1_btn.src.replace("_on", "_off");
    }
  }
}