Bootstrap手风琴头

Question

我在手风琴标题中添加了+ - 图像。页面加载时，+符号显示为粗体。点击后看起来很正常。是因为标题属性＆gt;如何解决？

<accordion-heading is-open="group.open">
                <div class="row" style="height:22px;">
                    <div class="col-lg-2 col-md-2 col-sm-4 col-xs-8">
                        <label class="aa-blue b h5">{{group.title}}</label>
                    </div>
                    <div class="col-lg-2 col-md-2 col-sm-4 col-xs-8">
                        <label class="aa-black b h5">{{group.stn}}</label>
                        <label class="aa-blue b h5">{{group.date}}</label>
                    </div>
                    <div class="col-lg-7 col-md-7 col-sm-12 col-xs-12">
                        <label class="h5">{{group.header|cut:true:60:' ...'}}</label>
                    </div>
                    <div class="col-lg-1 col-md-1 col-sm-2 col-xs-4">
                        <button class="btn btn-xs" ng-click="isCollapsed = !isCollapsed">
                            <i ng-class="{'glyphicon glyphicon-plus': isCollapsed, 'glyphicon glyphicon-minus': !isCollapsed}"></i>
                        </button>
                    </div>
                </div>
</accordion-heading>