Set height to auto plus 10%

Question

I am making a simple box and inner box. The outer box is white and the inner box is purple. The inner box width is static (95%, i understand this is not necessarily static, but in the context of the height you'll understand) but the height is set to auto to reflect the height of the content text. The trick I'm facing is having a margin on the bottom. It is easy to set the sides. The outer box width is set to 97%, and the inner box width is set to 95%. There is a 10% margin on the top. But since the inner box height is set to auto, the outer box ends vertically where the inner box does. Is there any way to have the height of the outer box set to auto + 10%? Or something similar? Thanks!

Answer 1

Billy Moat's answer was perfect! I used padding-bottom to get it to work.