Ok here's what I have copied from the post you quoted. I don't see any similar code to replace. I've tried to just paste it in the lower sections but obviously not working.
<!--
begin reorder .ProductItem-details-checkout child elements
SS Version : 7.1
the code is comprised of two style tags both of which must be present for the
effect to work. the second style tag is where the user controls the order of
elements
-->
<style>
/* no user serviceable parts below */
.ProductItem-details-checkout .product-quantity-input,
.ProductItem-details-checkout .product-variants,
.ProductItem-details-checkout .ProductItem-details-excerpt,
.ProductItem-details-checkout .ProductItem-product-price,
.ProductItem-details-checkout .sqs-add-to-cart-button-wrapper
{
-webkit-box-ordinal-group : unset;
-ms-flex-order : unset;
order : unset;
}
.ProductItem-details .ProductItem-details-checkout {
display : -webkit-box;
display : -ms-flexbox;
display : flex;
}
</style>
<style>
/* begin user reorder, this is where you get to control the order */
.ProductItem-details-checkout .product-quantity-input {
-webkit-box-ordinal-group : 2;
-ms-flex-order : 1;
order : 1;
}
.ProductItem-details-checkout .sqs-add-to-cart-button-wrapper {
-webkit-box-ordinal-group : 2;
-ms-flex-order : 1;
order : 1;
}
/* end user reorder */
</style>
<!-- end reorder .ProductItem-details-checkout child elements -->