How to set background color of view transparent in React Native

This is the style of the view that i have used

backCover: {
  position: 'absolute',
  marginTop: 20,
  top: 0,
  bottom: 0,
  left: 0,
  right: 0,
}

Currently it has a white background. I can change the backgroundColor as i want like '#343434' but it accepts only max 6 hexvalue for color so I cannot give opacity on that like '#00ffffff'. I tried using opacity like this

backCover: {
  position: 'absolute',
  marginTop: 20,
  top: 0,
  bottom: 0,
  left: 0,
  right: 0,
  opacity: 0.5,
}

but it reduces visibility of view’s content.
So any answers?