问题样式图像上传按钮

Question

基本上，我试图样式我的图片上传表单字段。根据这里另一个问题的指导，我最终做了以下工作：

document.getElementById("uploadBtn").onchange = function () { document.getElementById("uploadFile").value = this.value; };

.fileUpload {
    position: relative;
    overflow: hidden;
    margin: 10px;
  }
  .fileUpload input.upload {
    position: absolute;
    top: 0;
    right: 0;
    margin: 0;
    padding: 0;
    font-size: 20px;
    cursor: pointer;
    opacity: 0;
    filter: alpha(opacity=0);
  }

<input id="uploadFile" placeholder="Choose File" disabled="disabled"/>
                    <div class="fileUpload btn btn-primary">
                        <span>Upload</span>
                        <input id="uploadBtn" type="file" class="upload"/>
                    </div>