If any are interested in the same, I changed the front end CSS file to the following:
/* checkout address layout, 24th june changed checkout address width from 700pixels to 100%, adress left and right from width 350px to 50%*/
.hikashop_checkout_address{
clear:both;
width:100%;
margin:auto;
}
.hikashop_checkout_address_billing_only{
clear:both;
width:100%;
margin:auto;
}
.hikashop_checkout_billing_address{
}
.hikashop_checkout_address_left_part{
width:50%;
float:left;
}
.hikashop_checkout_address_right_part{
width:50%;
float:left;
}
This seems to work fine.