Building Responsive, Mobile-First Pages with Flint

Most traffic hits your pages on a phone first. First impressions form in seconds, and if the layout breaks or the copy is hard to read on a small screen, visitors leave before they ever see your value prop.

Flint pages are agent-driven and agent-created, which means great results come from two things working together: sound design principles and how you prompt the agent. A well-structured prompt signals the right constraints upfront so the agent builds for mobile from the start rather than retrofitting it later.

This guide is for anyone building landing pages with Flint — especially teams expecting traffic across a mix of devices.

Apply these principles when building or reviewing any page:

• •Design for the smallest screen first, then scale up. Single column beats multi-column on mobile almost every time. Let the layout expand as screen size grows, not the other way around.
• •Use one primary CTA, repeated as the visitor scrolls. Stacking competing buttons splits attention. Pick the one action you want and repeat it at natural scroll intervals.
• •Front-load the value prop above the fold. On mobile you have a few seconds before someone bounces. Lead with what you do and why it matters, not with preamble.
• •Keep copy short and scannable. Tight headlines, short paragraphs, and clear section breaks make content readable at a glance. Walls of text lose people fast on small screens.
• •Use large tap targets and generous spacing. Nothing frustrates a mobile visitor more than a button that's hard to hit with a thumb. Give interactive elements room to breathe.
• •Use readable type and strong contrast. Body text should be 16px or larger. Low-contrast combinations that look fine on a desktop monitor can become unreadable in bright sunlight on a phone.
• •Keep media light. Heavy hero images or autoplay video hurt load time on cell connections. Optimize images, avoid unnecessary autoplay, and test on a throttled connection if you can.

The clearest way to get mobile-first output is to say it directly and give the agent strong structural constraints to work from:

• •State the context up front. Tell the agent the page is mobile-first. A prompt like "Build this as a mobile-first page" sets the right frame from the start so the agent prioritizes single-column layout, large touch targets, and readable type without needing separate corrections.
• •Give the agent one source of structure to work from. Competing structural inputs — a rough wireframe and a reference page and a list of sections all at once — muddy the output. Pick one authority and stick to it.
• •Be specific about hierarchy. Tell the agent the one action you want visitors to take, what belongs above the fold, and roughly how many sections the page should have. Ambiguity on hierarchy is where most layout problems start.
• •Constrain it. One CTA. Short copy. A defined section count. Specificity gives the agent a tighter problem to solve and produces a cleaner first pass than an open-ended prompt.
• •Iterate section by section. Rather than asking for the full page in one prompt, build and refine one section at a time. You get tighter control and stronger results — and it's much easier to course-correct early than to rebuild from scratch.

Video is one of the most common places responsive layouts break. There are two cases to handle differently.

Standard inline video

Use this prompt when you have a video element embedded within a section — not as a full background:

Make the video element fully responsive. Set it to fill the width of its container using width 100% and height auto, and preserve its native aspect ratio (16:9) so it never stretches or crops on any screen. Add a max-width so it doesn't blow out on large desktop displays, and center it within the section. On mobile it should span the full container width with comfortable side padding. Do not use any fixed pixel width or height.

Full-width background or hero video

Use this prompt when the video is meant to fill an entire section as a background:

Make the background video fill its section fully on any screen using object-fit cover, so it scales to the container without stretching or leaving gaps. Keep it edge to edge on mobile and desktop, and make sure overlaid text and buttons stay readable on top of it.

• •Build and review one section at a time. You'll catch sizing and layout issues much faster when the scope is narrow.
• •When output isn't sizing the way you want, share the page for a quick review. If something looks off on mobile and you're not sure why, paste the page into the chat and describe the problem. A targeted fix is almost always faster than rebuilding.