CSS Code for a Buy Button

Hi guys,

I have linked my shop (woocommerce) in the app, everything works fine… but the Buy Button in the shop is not displayed. It exists, but it is white and the font too. It is totally invisible so to say. When you know where the button is it is clickable. ?? On the website it works and also if I call up the shop via website on my mobile phone, then the button is visible, but not within the app. Someone knows how to solve this riddle? ??