文本/图标重叠其他内容

Question

我有一个引导按钮，可以展开/显示无序列表。无序列表的子项在其下面的内容后面呈现，如下所示。

定义了z-index的唯一部分是下拉菜单类：

 <ul class="dropdown-menu btn-block" role="menu" aria-labelledby="591357bd3b522" style="padding-top: 0px; padding-bottom: 0px;">
                                        <li role="presentation" class="tigo-green widget-style" data-parent="591357bd3b522" data-style="tigo-green" data-style-name="green">
                        <span role="menuitem">green</span></li>
                                            <li role="presentation" class="tigo-blue widget-style" data-parent="591357bd3b522" data-style="tigo-blue" data-style-name="blue">
                        <span role="menuitem">blue</span></li>
                                            <li role="presentation" class="tigo-orange widget-style" data-parent="591357bd3b522" data-style="tigo-orange" data-style-name="orange">
                        <span role="menuitem">orange</span></li>
                                            <li role="presentation" class="tigo-red widget-style" data-parent="591357bd3b522" data-style="tigo-red" data-style-name="red">
                        <span role="menuitem">red</span></li>
                                            <li role="presentation" class="tigo-purple widget-style" data-parent="591357bd3b522" data-style="tigo-purple" data-style-name="purple">
                        <span role="menuitem">purple</span></li>
                                            <li role="presentation" class="tigo-brown widget-style" data-parent="591357bd3b522" data-style="tigo-brown" data-style-name="brown">
                        <span role="menuitem">brown</span></li>
                                            <li role="presentation" class="tigo-pink widget-style" data-parent="591357bd3b522" data-style="tigo-pink" data-style-name="pink">
                        <span role="menuitem">pink</span></li>
                                            <li role="presentation" class="tigo-grey widget-style" data-parent="591357bd3b522" data-style="tigo-grey" data-style-name="grey">
                        <span role="menuitem">grey</span></li>
                                            <li role="presentation" class="tigo-gold widget-style" data-parent="591357bd3b522" data-style="tigo-gold" data-style-name="gold">
                        <span role="menuitem">gold</span></li>
                                            <li role="presentation" class="tigo-lightblue widget-style" data-parent="591357bd3b522" data-style="tigo-lightblue" data-style-name="lightblue">
                        <span role="menuitem">lightblue</span></li>
                                    </ul>

这是默认的bootstrap下拉列表，通过用span替换内部A元素并添加背景颜色稍加修改。

可能导致这种情况的原因是什么？我已经调整了大量的HTML / CSS，并且无法让这一点变得让步。