Dear @LN
I hope i understand your problem and please correct me if i am wrong :)
The main content should start at 40% of the page's height, however because you want your client to have freedom to change picture we cannot target any one image specifically.
Screen Shot 2020-07-29 at 3.25.05 PM.png
Here in the picture above i have targeted to whole "grid" and increased its "padding-top" from 1% to 40% using "Custom CSS & HTML"
Does this suit your needs or is it too simple a solution?
Your client can still change the images and this will continue to use the 40%
I hope this sets you in the right direction!
https://www.khanacademy.org/computing/computer-programming/html-css
https://www.khanacademy.org/computing/computer-programming/html-css/web-development-tools/a/using-the-browser-developer-tools
These are two links that can introduce you to the basics of CSS if you having difficulty
As always thank you heaps for using Lay theme and having Patience with the Forum
Best wishes
Sincerely
Richard