I can not find a way to arrange the field “Prénom” and the field “Nom” to be on the same line.
I tried to modify the width, the type of box but I cannot manage it…
You’ll find it easier to layout your form if you group each of your label+input pairs in a containing DIV classes something like form-field ( flex, vertical ).
Then you can wrap those prenom and nom divs together in another div ( flex, horizontal ).
You may also want to set the form to flex, vertical.
FORM flex vertical
DIV flex horizontal
DIV.form-field flex vertical
LABEL prenom
INPUT
DIV.form-field flex vertical
LABEL nom
INPUT
DIV.form-field flex vertical
LABEL adresse
INPUT
etc.