Form fields are rendered strangely

Your software
My Mautic version is: 3.1.2
My PHP version is: 7.3
My Database type and version is: MySQL 5.7

Your problem
I created a form having 6 fields and put that onto a landing page. In the resulting page, the fields are not rendered under another but in two columns, which i do not want. Also the background of some fields is white and others are grey.
What have i done wrong? Looks like a fluid layout.