详解css边距重叠的几种解决方案

<div class="parent">
    <div class="child">
    </div>
</div>

.parent { 
    width: 300px;       
    height: 300px;
    border: 1px solid #ccc;
}
.child {
    width: 200px;
    height: 200px;
    margin: 20px;
}

.parent {
    padding： 1px;
    width: 300px;
    height: 300px;
}
.child {
    width: 200px;
    height: 200px;
    margin: 20px;
}

<div class="parent">
     <div style="width: 20px;height: 20px;margin-top: "></div>
     <div class="child">
     </div>
</div>

.parent {
    overflow: hidden;
    width: 300px;
    height: 300px;
}
.child {
    width: 200px;
    height: 200px;
    margin: 20px;
}

.parent {
    width: 300px;
    height: 300px;
} 
.child {
    width: 200px;
    height: 200px;
    margin: 20px; 
    display: inline-block;
}