css fixed視窗底部固定定位

前言已經不想說了，直接貼程式碼吧

    <div class="btn_box box1" id="box1">
        <button  class="btn_confirm" id="btn_confirm">確認</button>
    </div>

.btn_box {
    width: 100%;
    position: fixed;
    display: flex;
    align-items: center;
}
.box1 {
    bottom: 6.80rem;
}
.btn_confirm {
    width: 19.69rem;
    height: 3.06rem;
    background: #cccccc;
    border-radius: 0.31rem;
    font-size: 0.94rem;
    font-family: PingFangSC-Medium, PingFang SC;
    color: #FFFFFF;
    margin: 0 auto;
}