div3不加浮动就好了，不想左侧有80像素藏在div2下边的话，div3加 margin-left:80px;
记得采纳，谢谢
*{ margin:0; padding:0;}
.div0{background-color: aquamarine;border: dotted #FF0505 1px;width: 800px;height: 800px;}
.div1{width: 100%;height: 100px;border: inherit #F9061C 1px;background-color: red;margin-top: 0px;float: left}
.div2{width: 80px;height: 80px; border: #AF2fff solid 1px;background-color: cadetblue;margin-top:10px;float: left}
.div3{width:700px; /*这里div3宽度取值要满足：div1宽度“ > ”或“ = ”div2 + div3*/
height: 20px;border: #00f0f0 solid 1px;background-color: blue;float: left;margin-top: 10px}
.divt{width: 100%;height: 100px}
