Your visual language is a foundation, not a polish layer. Lovable needs to know the look and feel early, otherwise your interface might function but feel totally wrong. Don't fix design problems later, decide them up front.
Choose a direction — calm and elegant, bold and disruptive, premium and sleek — then feed it into your prompt using buzzwords, tone descriptors and UI patterns.
Prompt
Use a calm, wellness-inspired design. Soft gradients, muted earth tones, round corners, and generous padding. Font is 'Inter'. Overall tone should feel gentle and reassuring.
You don't prompt your way into good design. You prompt from it.