Responsive Storefront

Overview

Apply mobile-first responsive design patterns to a commerce storefront so that the shopping experience is fast and usable on phones, where the majority of commerce traffic originates. Key patterns include thumb-zone aware layouts, a sticky buy bar that appears on scroll, tap-target sizing, and responsive product grids that reflow without horizontal scrolling.

When to Use This Skill

When more than 50% of storefront traffic comes from mobile devices (check your analytics)
When building a new storefront from scratch and laying out the CSS architecture
When auditing an existing storefront for mobile usability issues
When implementing a product detail page and need a sticky buy button pattern
When optimizing mobile conversion rate and cart abandonment

Core Instructions

Step 1: Determine the merchant's platform and choose the right approach

Platform	Recommended Approach	Why
Shopify	Use a mobile-first OS2.0 theme (Dawn, Sense, Craft) — all are responsive by default; configure mobile layout in Theme Editor	Dawn scores 90+ on mobile PageSpeed out of the box; the Theme Editor exposes mobile-specific layout controls
WooCommerce	Use a mobile-first WooCommerce theme (Astra, Kadence, or Flatsome) — all include responsive breakpoints and mobile cart drawer built in	Astra and Kadence score well on Core Web Vitals; Flatsome has built-in sticky header and mobile menu without plugins
BigCommerce	Use Cornerstone theme which is mobile-first by design; configure breakpoints in Theme Editor	Cornerstone is BigCommerce's reference theme and passes Google's mobile usability tests
Custom / Headless	Write mobile-first CSS with `min-width` media queries and build a responsive product grid, sticky buy bar, and bottom-sheet cart drawer	Full control over all breakpoints and touch interactions; see patterns below

Step 2: Configure mobile layout on your platform

Shopify

Theme Editor mobile configuration:

Go to Online Store → Themes → Customize
Click the Mobile preview icon in the top toolbar to preview on a phone
Configure Header settings:
- Set Mobile menu type: Drawer (recommended) or Dropdown
- Enable Sticky header so navigation stays visible while scrolling
Configure Collection page:
- Set Products per row (mobile) to 2 (standard) or 1 (large cards)
- Enable Filters as a drawer on mobile (not sidebar)
Configure Product page:
- Enable Sticky add-to-cart in the product section settings
- Set Media placement to stack gallery above product info on mobile (this is the default)
In Theme settings → Buttons, set button height to at least 44px to meet touch target requirements

Testing mobile performance:

Open Google PageSpeed Insights (pagespeed.web.dev) and enter your store URL
Review the Mobile tab — aim for 75+ Performance score
The most common fix: compress images via Settings → Files and replace large images with WebP versions

WooCommerce

Astra theme mobile configuration:

Go to Appearance → Customize → Header → Mobile Header
Configure hamburger menu style and position
Under Appearance → Customize → WooCommerce → Shop Page, set Products per row (mobile) to 2
Under Appearance → Customize → WooCommerce → Product Page, enable Sticky Add to Cart bar for mobile
In Appearance → Customize → Global → Container, ensure container width is 100% on mobile (no horizontal padding issues)

Kadence theme mobile configuration:

Go to Appearance → Customize → WooCommerce → Product Archive
Set mobile columns to 2 and configure card spacing
Under Appearance → Customize → WooCommerce → Product Page, enable Sticky Add to Cart
In Kadence → Header Builder, configure the mobile header layout — Kadence lets you drag elements (logo, menu, cart) to separate mobile header rows

Flatsome theme:

In Theme Options → WooCommerce → Products, configure mobile product grid columns
Enable Sticky Add to Cart in Theme Options → WooCommerce → Product
Flatsome's UX Builder has a mobile preview mode — use it to inspect every page's mobile layout

BigCommerce

Cornerstone mobile configuration:

Go to Storefront → My Themes → Customize
Preview on mobile using the device icon in the toolbar
Under Global → Layout, configure mobile breakpoints and container padding
Under Product Page → Images, set gallery layout to Stacked on mobile (image above product info)
Enable Mobile overlay for the cart — this converts the cart from a sidebar to a bottom sheet on mobile
Under Category Page → Product Cards, set mobile columns to 2

Custom / Headless

Mobile-first CSS foundations:

/* tokens.css */
:root {
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --touch-target: 44px;     /* WCAG 2.5.5 minimum tap target */
  --content-max-width: 1200px;
}

/* Breakpoints: sm=640px, md=768px, lg=1024px */
/* Write base styles for mobile, add min-width queries for larger screens */

Responsive product grid (auto-fills columns based on available width):

.product-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(min(160px, 100%), 1fr));
  gap: var(--space-md);
  padding: var(--space-md);
}

@media (min-width: 640px) {
  .product-grid { grid-template-columns: repeat(auto-fill, minmax(200px, 1fr)); }
}

@media (min-width: 1024px) {
  .product-grid { grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: var(--space-lg); }
}

/* Minimum 44px touch target on product card CTA */
.product-card__cta { min-height: var(--touch-target); display: flex; align-items: center; }

Sticky buy bar — appears when primary Add to Cart scrolls out of view:

export function StickyBuyBar({ product, onAddToCart }) {
  const [visible, setVisible] = useState(false);

  useEffect(() => {
    const primaryBtn = document.getElementById('main-add-to-cart');
    if (!primaryBtn) return;
    const obs = new IntersectionObserver(([e]) => setVisible(!e.isIntersecting));
    obs.observe(primaryBtn);
    return () => obs.disconnect();
  }, []);

  return (
    <div className={`sticky-buy-bar ${visible ? 'visible' : ''}`} aria-hidden={!visible}>
      <img src={product.image} alt="" width="40" height="40" />
      <span>{product.name}</span>
      <span>${product.price}</span>
      <button onClick={onAddToCart} tabIndex={visible ? 0 : -1}>Add to Cart</button>
    </div>
  );
}

.sticky-buy-bar {
  position: fixed; bottom: 0; left: 0; right: 0;
  background: #fff; border-top: 1px solid #e2e8f0;
  transform: translateY(100%); transition: transform 0.2s ease; z-index: 50;
  padding-bottom: env(safe-area-inset-bottom); /* iPhone home indicator */
  display: flex; align-items: center; gap: 0.5rem; padding: 0.75rem 1rem;
}
.sticky-buy-bar.visible { transform: translateY(0); }

Mobile cart drawer (bottom sheet pattern):

.cart-drawer {
  position: fixed; right: 0; top: 0; bottom: 0;
  width: min(400px, 100vw); background: #fff;
  transform: translateX(100%); transition: transform 0.3s ease;
  overflow-y: auto; overscroll-behavior: contain;
}

@media (max-width: 640px) {
  .cart-drawer {
    top: auto; width: 100vw; height: 85vh;
    transform: translateY(100%); border-radius: 16px 16px 0 0;
  }
  .cart-drawer.open { transform: translateY(0); }
}

.cart-drawer.open { transform: translateX(0); }

/* Checkout button stays within thumb reach */
.cart-checkout-btn {
  position: sticky; bottom: 0; background: #fff;
  padding: var(--space-md);
  padding-bottom: calc(var(--space-md) + env(safe-area-inset-bottom));
}

Global 44px touch targets:

button, a, input[type="checkbox"], input[type="radio"], select, [role="button"] {
  min-height: var(--touch-target);
  min-width: var(--touch-target);
}

Best Practices

Write mobile-first CSS — start with the smallest screen styles and add min-width media queries to enlarge; the reverse approach leads to specificity conflicts
Use env(safe-area-inset-bottom) — required for iPhone notch/home indicator; without it, bottom-fixed buttons are obscured
Test with real devices — browser DevTools emulation does not replicate iOS Safari's dynamic viewport height or touch scroll inertia
Use overscroll-behavior: contain on scroll containers — prevents body scroll from leaking when users swipe in the cart drawer
Use 100dvh instead of 100vh on full-screen elements — iOS Safari's dynamic toolbar causes 100vh to include the toolbar height, causing overflow
Set font-size to at least 16px on <body> — prevents iOS Safari from auto-zooming on input focus

Common Pitfalls

Problem	Solution
Sticky buy bar obscures footer or checkout button	Hide the bar when the footer or checkout button enters the viewport using IntersectionObserver
iOS Safari layout jumps when toolbar appears	Use `100dvh` (dynamic viewport height) instead of `100vh`; fall back with `@supports (height: 100dvh)`
Font too small to read without pinch-zooming	Set `font-size: 1rem` (16px) on body; never set it lower on mobile
Cart drawer body scroll	Apply `overflow: hidden` on `<body>` when drawer is open; restore on close
Product images load slowly on mobile	Specify `width` and `height` attributes to prevent layout shift; use `loading="lazy"` for below-fold images

Related Skills

@mega-menu-builder
@quick-view-modal
@accessibility-commerce
@storefront-theming

responsive-storefront