Hi,
Unfortunately, such modifications cannot be made using simple custom CSS code. The button needs to be moved to another block and should have different CSS classes. To achieve this, the product grid template HTML structure must be significantly altered, which would also break other options related to the product design, and such changes are out of our theme support scope.
However, our theme offers 11 different product designs, and to implement your idea, you can choose another product design where the button is already positioned at the bottom of the product along with the quantity buttons next to it, for example, the “Standard button” design: (screenshot https://monosnap.com/file/RsWiaSBF83hzsQBFIkamKn4ha79pzM).
Regards
.
