display:block 让块级元素变成行级元素。而display:inline则相反。如：
span默认是块级元素
div默认是行级元素
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<style>
.boder{border: 1px solid #666;}
</style>
</head>
<body>
<div class="boder">
<span>我是块级元素</span>
<span>我是块级元素</span>
</div>
<div class="boder">
<span style="display:block;">我被加了“display:block;”，变成行级元素</span>
<span style="display:block;">我被加了“display:block;”，变成行级元素</span>
</div>
</body>
</html>