<!DOCTYPE html>
<html>
<head>
    <style type="text/css">
       .div1{
          width:30%;
          height:100px;
          background-color:red;
          float:none;
        }
       .div2{
          width:40%;
          height:100px;
          background-color:green;
          float:left;
        }
    </style>
</head>
<body>
    <div class="div1"></div>
    <div class="div2"></div>
</body>
</html>
Mặc định float:left;