Remove border in Native Base Thumbnail

I am using a thumbnail where the cross is transparent so to give it a white background color, I added it in its style. However, a white border line also appears. How can I remove this?

export const Screen: React.FunctionComponent = () => {  return (<SafeAreaView style={styles.safeAreaViewContainer}><View style={styles.container}><View style={styles.iconsContainer}><TouchableOpacity          style={styles.cross}><Thumbnail  style={styles.thumbnail}            source={{              uri:'https://cdn0.iconfinder.com/data/icons/very-basic-android-l-lollipop-icon-pack/24/close-512.png',            }}          /></TouchableOpacity></View></View></SafeAreaView>  );};export const styles = StyleSheet.create({  safeAreaViewContainer: {    flex: 1,  },  container: {    backgroundColor: '#323443',    flex: 1,  },cross: {    paddingTop: moderateScale(30),    paddingLeft: moderateScale(20),    zIndex: 100,  },  thumbnail:{    backgroundColor: 'white',  }});