用的是Vant的NavBar插件：

https://youzan.github.io/vant-weapp/#/nav-bar#wai-bu-yang-shi-lei

效果图

页面使用，放开注释的地方就可以显示左边按钮

<van-nav-bar title="精益成本核算" fixed="true" placeholder="true" custom-class="nav" title-class="nav-title"><!-- <view slot="left" class="leftIcon"><van-icon name="arrow-left" color="white" size="15px" /></view> -->
</van-nav-bar>

全局样式

.nav{background-color: #0081FF !important;
}
.nav-title{color: white !important;
}