That doesn't seem like it makes sense. Why would you want the right edge of this button extending beyond its container and going off the screen?  Between this and the width setting, you've ended up with a button that has a visible width of 25% - 4rem.  On a 320px wide screen that is 40px wide, which seems just right for a 30x30 pixel image.  But if that is the size you want, then the 25% business doesn't make sense.