<style> .main{min-height: 700px;} </style> <div class="header"></div> <div class="main"></div> <div class="footer"></div>
<body> <style> body{position: relative;height: 1000px;} .footer{position: absolute;bottom: 0;left: 0;height: 20px;width: 100%;background-color: yellow;} </style> <div class="header"></div> <div class="main"></div> <div class="footer"></div> </body>