*{

                margin: ;

                padding: ;

            }

            div{

                text-align: center;

                font-size: 30px;

            }

            .header,.footer{

                width: %;

                height: 100px;

                line-height: 100px;

                background-color: red;

            }

            .content{

                width: %;

                position: absolute;

                top: 100px;

                bottom:100px;

                background-color: yellow;

            }

            .footer{

                position: absolute;

                bottom: 0px;

            }

         <div class="header">头部</div>

        <div class="content">内容</div>

        <div class="footer">底部</div>