Set height to auto plus 10%

I make a simple drawer and an inner drawer. The outer box is white and the inner box is purple. The inner width of the window is static (95%, I understand that this is not necessarily static, but in the context of the height that you will understand), but the height is set to auto to reflect the height of the content text. The trick I come across has an edge at the bottom. Easy to set sides. The width of the outdoor unit is set to 97%, and the width of the indoor unit is 95%. Upstairs there is a 10% margin. But since the height of the inner box is set to auto, the outer box ends vertically where the inner box is. Is there any way for the height of the outer box to be set to auto + 10%? Or something similar? Thank!