Hi Nicolas,
1. Here is a simple example of CSS code to arrange the checkout form into 2 coulmns:
@media(min-width:991px){
section#mphb-customer-details {
display:flex;
flex-direction:row;
flex-wrap:wrap;
}
section#mphb-customer-details p{
width:50%;
}
}
If you need an advanced layout customization you may contact us and discuss it as a custom order.
2. Could you please provide the page URL where you wish to align the calendar to the center?