控制ul中被选中的li标签保持在可视范围

                <div class="weixiu">
                            <span id="sjxh">选择需要维修的设备</span>
                            <input type="hidden" id="myself_data" value="" style="display: none">
                            <s></s>
                            <div id="weixiu-cotent">
                                <div id="weixiu-dropdown-content" class="dropdown-content">
                                    <ul id="weixiu_ul">
                                    </ul>
                                </div>
                                <div id="xh1" class="sj-dropdown-content">
                                    <ul id="xh1_ul" style="overflow-y:scroll;">
                                    </ul>
                                </div>
                                <div class="color-dropdown-content" id="color-dropdown">
                                    <ul>
                                    </ul>
                                </div>
                            </div>
                        </div>
                <div class="weixiu">