自定义标签栏，每个标签中有两个图像使用反应导航？

I am creating an app using React Native for ios. Instead of having an active tintColor I want to have two little triangles (another image/icon) which appears when you are on the selected tab. It is important that the center y axis of the triangles is = to the y axis of the bottom of the tabbar image and that the tab icon is in the center of the triangles as seen below. At the moment I have the tab bar, the icons and navigation working - I just don't know how to make the triangles appear:I am creating an app using React Native for