我的css和老師一樣，但是為什么會偏離位置？

.index-menu{
	border-top:6px?solid?#f34949;
	position:?relative;
}
.index-menu?.menu-tips{
	position:?absolute;
	top:?0;
	left:?50%;
	margin-left:?-78px;
	width:?156px;
	height:?71px;
	background:?#f34949;
	color:?#fff;
	text-align:?center;
	line-height:?65px;
	font-size:?20px;
}
.index-menu?.menu-tips:after{
	width:?0;
	height:?0;
	content:?"";
	position:?absolute;
	bottom:?0;
	left:?0;
	border-left:?78px?solid?transparent;
	border-right:?78px?solid?transparent;
	border-bottom:?10px?solid?#fff;
}