function toggle_visibility() {
       var e = document.getElementById("currentwork");
	   var f = document.getElementById("previousbutton");
	   var g = document.getElementById("previouswork");
	   var h = document.getElementById("currentbutton");
       if(e.style.display == 'block'){
          e.style.display = 'none';
		  g.style.display = 'block';
		  f.style.display = 'none';
		  h.style.display = 'block';
       }else{
          e.style.display = 'block';
		  g.style.display = 'none';
		  f.style.display = 'block';
		  h.style.display = 'none';
	   }
	}