SOURCE

<div class="btn btn-upload">
  <span>点击上传</span>
  <input type="file"/>
</div>

.btn {
  font-size: 14px;
  border: 1px solid;
  border-radius: 4px;
  padding: 5px 10px;
}
.btn:hover {
  color: blue;
}

.btn-upload {
  position: relative;
  display: inline-block;
  overflow: hidden;
}
.btn-upload input {
  position:absolute;
  right: 0px;
  top: 0px;
  opacity: 0;
  -ms-filter: 'alpha(opacity=0)';
  font-size: 200px;
  cursor: pointer;
}