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<p class="notaffected">这个p元素在浮动元素前，它不受影响</p>
<div class="box1">box1</div>
<div class="box2">box2</div>
<p class="notaffected">这个p元素在浮动元素box2之后并且是紧邻其后的元素，受影响</p>

.box1{
    height:100px;
    background:#99FF33;
    float:left;
}
.box2{
    height:100px;
    background:#FF99FF;
    float:left;
}
.notaffected{
    background:lightgray;
}