python中如何使用find_element_by_css_selector() 定位网页

如上图的，利用python定位到左边的按钮，源码如下，如何定位，请各位大神指点。谢谢！

<div class="pageHeader" style="background: #E1E1E1; height: 68px; position: relative;">
        <span class="button" οnclick="AnalysisDialog().Show();" style="position: relative; top: 22px; left: 10%;">
            START NEW ANALYSIS
        </span>

        <span class="button" οnclick="SearchDialog().Show();" style="position: relative; top: 22px; left: 10%; margin-left:20px">
            SEARCH REPORTS
        </span>

        
        <span class="button" οnclick="window.open('Applets/QCAP.jnlp');" style="position: relative; top: 22px; left: 10%; margin-left:20px">
            QCAP 2.0 BETA
        </span>
        
    </div>