我一直用浮动。认识到也许它不是最好的方法。尝试使用相对位置。为什么 myDiv 的孩子不互相忽略 top ?因为它不是 inline-block ?
<div class="myDiv">
    <div class="myDiv1"></div>
    <div class="myDiv2"></div>
    <div class="myDiv3"></div>
    <div class="myDiv4"></div>
</div>
.myDiv
{
    float: left;
    margin-left: 10px;
    margin-top: 10px;
    width: 100px;
    height: 100px;
    background-color: grey;
}
.myDiv1
{
    background-color: green;
    width: 10px;
    height: 10px;
    position: relative;
    top: 10px;
    left: 10px;
}
.myDiv2
{
    background-color: red;
    width: 10px;
    height: 10px;
    position: relative;
    top: 0px;
    left: 30px;
}
.myDiv3
{
    background-color: blue;
    width: 10px;
    height: 10px;
    position: relative;
    top: 0px;
    left: 50px;
}
.myDiv4
{
    background-color: yellow;
    width: 10px;
    height: 10px;
    position: relative;
    top: 0px;
    left: 70px;
}