code: func (b *Box) FillWithPercentageMargins(container *Box, horizmarginp float32, vertmarginp float32) {
  	horizmargin := int(float32(container.inner.W) * horizmarginp)
  	vertmargin := int(float32(container.inner.H) * vertmarginp)
  	b.Fill(container)
  	b.frame.X += horizmargin
  	b.frame.Y += vertmargin
  	b.frame.W -= horizmargin * 2
  	b.frame.H -= vertmargin * 2
  }
docs: // Place a Box inside a given container, using the given percentage wise ratios.
  // horizmarginp can for example be 0.1 for a 10% horizontal margin around
  // the inner box. vertmarginp works similarly, but for the vertical margins.