pic1 = new Image(); 
pic1.src = "assets/btn_home_on.png"; 
pic2 = new Image(); 
pic2.src = "assets/btn_patients_on.png"; 
pic3 = new Image(); 
pic3.src = "assets/btn_hcp_on.png";
pic4 = new Image(); 
pic4.src = "assets/btn_investigators_on.png";