window.onload = function() { 
middle_panel(); 
} 


function middle_panel() { 
  
	var middle_panel = document.getElementById('middle_panel');
    
	var middle_panel_height = middle_panel.offsetHeight;
	
 
    if (middle_panel_height < 400){
 
      middle_panel.style.height = 400 + "px";
 
    }
   
}