为什么我的标题和导航会低于我的英雄图像？每当我增加图像上文本的大小时，导航和标题就会进一步下降。如果我去掉文本的大小，它会回到我想要的位置。这是我的html和css。
HTML
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>Amanda Farrington</title>
<link rel="stylesheet" href="css/demo.css" />
<link href='http://fonts.googleapis.com/css?family=Roboto:400,300,500' rel='stylesheet' type='text/css'>
</head>
<body>
<div id="header">
<div id="leftHeader">
<img src="assets/logo2.jpg" alt="Logo" style="width:65px;height:65px">
<h1>Amanda Farrington</h1>
</div>
<div id="nav">
<ul>
<li><a href="index.html">About</a></li>
<li><a href="tips.html">Work</a></li>
<li><a href="mentally.html">Contact</a></li>
</ul>
</div>
</div>
<div id="hero">
<div id="heroImage">
<img src="assets/trees.jpg" alt="trees" style="width:100%;height:10%">
</div>
<div id="overlay">
<h2>Amanda Farrington</h2>
</div>
</div>
</body>
</html>
CSS
body {
margin: 0px;
padding: 0px;
height: 100%;
background: white;
}
#header {
color: #D7DADB;
font-family: 'Roboto', sans-serif;
font-weight: 300;
font-size : 15px;
text-align: left;
width: 97%;
margin:0;
padding-left: 3em;
float: left;
background: white;
height: 10%;
}
#leftHeader
{
}
#header img
{
float: left;
padding-left: 3em;
}
h1{
width: 9em;
float: left;
padding-left: 0.5em;
color: #45CCCC;
padding-bottom: 1px;
}
#nav {
width: 40%;
margin:0;
padding:0;
text-align: right;
color: red;
font-size:20px;
float: right;
padding-right: 2em;
}
#nav ul {
padding: 1px;
}
#nav li {
display: inline;
padding: 38px;
}
#nav li a {
color: #2C3E50;
text-decoration: none;
}
#nav li a:hover {
color: #45CCCC;
}
#hero{
width: 100%;
height: 30em;
}
#heroImage
{
top: 12%;
width: 100%;
z-index: 1;
position: absolute;
}
#overlay{
width: 30em;
top: 90%;
margin-left: 30%;
z-index: 2;
position: relative;
}
h2{
width: 9em;
position: relative;
font-family: 'Roboto', sans-serif;
font-weight: 300;
font-size: 60px;
float: center;
color: white;
opacity: 1.0;
text-shadow: 2px 2px 3px rgba(0,0,0,0.6);
}
这是因为你的#heroImagediv的position: absolute;（如果我理解，你想要什么）