I have tried to show you the picture of how to deal with the Design It Part of the Form Builder in MailChimp in details. I think it will help you design your form the way it suits you. It is a step by step teaching I hope it helps you.

Design It Tab has the Page, Body, Forms, or MonkeyRewards tabs that help to edit the style, color, font, and graphics, also edit the page and frame layout of your signup form and response emails.

The page section is where you make changes to the background, header, and wrapper to your form.

In the body section, you can change the foreground color and set the font and link style.

The forms section is where you change the button styling and choose the font styles for your fields, help texts and error text.

The last part is the monkey rewards badge. From here, you can change the monkey award badge that appears on your form and response email. The badge is required on free accounts but can be turned off or on for paid accounts.

Please like.