小编Ger*_*ann的帖子

#outer {
  width: 90%;
  height: 90%;
  margin: 5%;
  overflow: auto;
  background-color: red;
}

.inner1 {
  float: left;
  width: 150px;
  height: 150px;
  margin-right: 20px;
  background-color: blue;
}

.inner2 {
  float: left;
  width: 150px;
  height: 150px;
  margin-right: 20px;
  background-color: blue;
}

.inner3 {
  float: left;
  width: 150px;
  height: 150px;
  background-color: blue;
}

<div id="outer">
  <div class="inner1">1</div>
  <div class="inner2">2</div>
  <div class="inner3">3</div>
</div>