只要加上 ::v-deep 即可解决：

<style lang="scss" scoped>
	/* ::v-deep加上样式前面 */
    ::v-deep .el-transfer {
        display: flex;
        align-items: center;
        .el-transfer-panel {
            width: calc((100% - 200px) / 2);
        }
        .el-transfer__buttons {
            text-align: center;
            width: 200px;
        }
    }
</style>