window.onload = function
 
(){
                var bx1 = document.getElementById("box1");
                document.querySelector(".btn1").onclick = function(){
                    bx1.style.height = "400px";
                    bx1.style.width = "400px";
                    bx1.style.backgroundColor = "red";
                    
                }
                
                document.querySelector(
 
".btn2").onclick = function(){
                    if(window.getComputedStyle){
                        // 正常瀏覽器
                        alert(getComputedStyle(bx1,null).backgroundColor);
                    }else{
                        //IE8
                        alert(bx1.currentStyle.backgroundColor);
                    }
                    
                }
            }