Easterbox for my wife

select the template and click on edit node
then remove the nodes that protrude to create a straight line 

add your design and customize it
click on the template and select outline with 0mm 
this creates a copy in the same place

selcet both and click unite

remove the inner nodes 
click edit node again and select one of the inner nodes and hold the remove button 

create a copy of your design to cut it out afterwards

add new design