js改变样式效果

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style type="text/css">
			#box{
				border: 1px solid #006633;
			}
		</style>
		<script type="text/javascript">
			window.onload = function(){
				var box = document.getElementById('box');
				var bgCol = document.getElementById('bgCol');
				var bgTxt = document.getElementById('bgTxt');
				var bgWi = document.getElementById('bgWi');
				var bgHe = document.getElementById('bgHe');
				var btnCol = document.getElementById('btnCol');
				var btnTxt = document.getElementById('btnTxt');
				var btnWi = document.getElementById('btnWi');
				var btnHe = document.getElementById('btnHe');
				
				// console.log(typeof bgCol);	判断类型
				// 背景
				btnCol.onclick = function(){
					var bgColol = bgCol.value;
					box.style.backgroundColor = bgColol;
					// console.log(bgColol);
				}
				// 文字颜色
				btnTxt.onclick = function(){
					var btnT = bgTxt.value;
					box.style.color = btnT;
					// console.log(btnT);
				}
				// 宽度
				btnWi.onclick = function(){
					var btnW = bgWi.value;
					box.style.width = btnW;
					console.log(btnW);
				}
				// 高度
				btnHe.onclick = function(){
					var btnH = bgHe.value;
					box.style.height = btnH;
					console.log(btnH);
				}
				
				
			}
		</script>
	</head>
	<body>
		<div id="box">
			中华人民共和国万岁！
		</div>
		<p><input type="text" name="" id="bgCol" value="" placeholder="请输入背景颜色"/><button type="button" id="btnCol">修改背景颜色</button></p>
		<p><input type="text" name="" id="bgTxt" value="" placeholder="请输入文字颜色"/><button type="button" id="btnTxt">修改文字颜色</button></p>
		<p><input type="text" name="" id="bgWi" value="" placeholder="请输入宽度"/><button type="button" id="btnWi">修改宽度</button></p>
		<p><input type="text" name="" id="bgHe" value="" placeholder="请输入高度"/><button type="button" id="btnHe">修改高度</button></p>
	</body>
</html>