Hi Philip!
The reason that your inputs are to big has to do with your theme "mai-engine". The plugin adds padding to the inputs that make the inline styles calculate a height and width that makes the inputs look off. When using any of the supported themes twentytwenty or twentytwentythree the inputs are shown correctly.
If you could add some custom CSS to the theme this should solve it.
body .mce-combobox .mce-textbox, body .mce-container-body .mce-textbox {
padding: 0;
}
Regards,
Joakim @ Simple:Press