SOURCE

<div class="box">
    基线对齐<button class="btn btn-primary">按钮</button>基线对齐
</div>
<div class="box">
    居中对齐<button class="btn btn-primary vertical-align-middle">按钮</button>居中对齐
</div>

.btn {
            display: inline-block;
            margin-bottom: 0;
            font-weight: normal;
            text-align: center;
            white-space: nowrap;
            touch-action: manipulation;
            cursor: pointer;
            border: 1px solid transparent;
            padding: 16px 12px;
            font-size: 48px;

        }

        .btn-primary {
            color: #fff;
            background-color: #337ab7;
            border-color: #2e6da4;
        }

        .box + .box {
            margin-top: 10px;
        }

        .vertical-align-middle {
            vertical-align: middle;
        }