How should I lay out the calculator in Webflow?
Give the calculator its own section with a max-width container, auto height and no overflow clipping. The calculator sizes itself to the space it gets, so the container decides how it looks. A width similar to your main reading column usually works well on desktop, and full width with modest padding on mobile.
Because the inline embed renders in an isolated container, Webflow classes don't style the calculator itself. Use them for the surrounding section only, and match the calculator's look with its theme, palette and fonts in your account.