style.css
#child1 {
fload: left;
}
#child2 {
fload: right;
}
.clearfix {
zoom: 1;
}
.clearfix:after {
content: ".";
display: block;
clear:both;
visibility: hidden;
}
index.html
<div class="clearfix">
<p id="child1">子要素1</p>
<p id="child2">子要素2</p>
</div>