SOURCE

<div id="parent">
  <div id="col1">
    <div class="inner">
    </div>
  </div>
  <div id="col2">
    <div class="inner">
    </div>
  </div>
  <div id="col3">
    <div class="inner">
    </div>
  </div>
  <div id="col4">
    <div class="inner">
    </div>
  </div>
</div>

#parent {
  margin-left: -10px;
}

#col1,
#col2,
#col3,
#col4 {
  float: left;
  width: 25%;
  box-sizing: border-box;
  padding-left: 10px;
}

#col1 .inner {
  background-color: red;
  height: 300px;
}

#col2 .inner {
  background-color: yellow;
  height: 300px;
}

#col3 .inner {
  background-color: green;
  height: 300px;
}

#col4 .inner {
  background-color: pink;
  height: 300px;
}