<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<style>
body {
margin: 0px;
padding: 0px;
}
.if-top {
display: block;
border: none;
width: 100%;
height: 120px;
}
.if-menu {
width: 20%;
border: none;
}
.if-content {
width: 78%;
border: none;
}
</style>
</head>
<body>
<iframe class="if-top" src="top.html"></iframe>
<iframe class="if-menu" src="menu.html"></iframe>
<iframe class="if-content" src="content.html"></iframe>
</body>
</html>
在上面的top iframe里面加上
display: block;