how reserve height while display is none

if you can use visiblity hidden property instead of display:none you can achieve what you want.

When you do visibilty:hidden it just make the elements opacity to 0 while the element is still retaining its space.

Use visibility: hidden instead of display: none. Your element won't display, but its dimensions still apply and affect other elements because it's still a part of the page flow.

Instead of putting display: none; on your div, put visibility: hidden;. It will be invisible, but still take up space.