Twitter Bootstrap에서 파일 업로드 버튼의 스타일을 어떻게 지정합니까?

<label class="btn btn-default">
    Browse <input type="file" hidden>
</label>

[hidden] {
  display: none !important;
}

<span class="btn btn-default btn-file">
    Browse <input type="file">
</span>

.btn-file {
    position: relative;
    overflow: hidden;
}
.btn-file input[type=file] {
    position: absolute;
    top: 0;
    right: 0;
    min-width: 100%;
    min-height: 100%;
    font-size: 100px;
    text-align: right;
    filter: alpha(opacity=0);
    opacity: 0;
    outline: none;
    background: white;
    cursor: inherit;
    display: block;
}