Storefront Theming

Overview

Architect a theming system using design tokens and CSS custom properties that allows a storefront to be re-skinned for multiple brands without modifying component code. Covers the token taxonomy (color, typography, spacing, radius), runtime theme switching for dark mode, and white-label multi-tenant architecture where each tenant supplies their own token overrides.

When to Use This Skill

• When building a platform that will power multiple branded storefronts from a single codebase
• When implementing dark mode for a storefront
• When a rebrand requires changing colors across thousands of component instances without hunt-and-replace
• When handing off a design system to a team that needs to maintain brand consistency

Core Instructions

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

Platform	Recommended Approach	Why
Shopify	Use the Theme Editor's Color scheme system + edit config/settings_schema.json and assets/base.css to add custom CSS variables	Shopify OS2.0 themes expose all brand colors, fonts, and border radii as Theme Editor settings that write to CSS variables automatically; no build step required
WooCommerce	Use the WordPress Global Styles system (WordPress 5.9+) with a block theme, or configure CSS variables in Appearance → Customize → Additional CSS for classic themes	Block themes using theme.json support a full design token system natively; classic themes need CSS custom properties added manually
BigCommerce	Configure theme settings in Storefront → My Themes → Customize — Cornerstone exposes colors, fonts, and spacing as Theme Editor variables; advanced customization via config.json and SCSS	Cornerstone compiles SCSS with Handlebars template variables; custom CSS variables can be added to the global stylesheet
Custom / Headless	Build a three-tier token system (global → semantic → component) using CSS custom properties, compiled from JSON using Style Dictionary	Full control over token taxonomy, dark mode, and multi-tenant overrides; see implementation below

Step 2: Configure theming on your platform

---

Shopify

Using the Theme Editor color system (no code required):

1. Go to Online Store → Themes → Customize
2. Click Theme settings (paint bucket icon) in the left panel
3. Under Colors, configure your brand's:
   • Primary, secondary, and accent colors
   • Background colors
   • Text colors
   • Button colors and text
4. Under Typography, set your font families and sizes
5. Under Buttons and inputs, configure border radius for buttons and form fields
6. All changes write to CSS custom properties that every component in the theme uses — no component-level changes needed

Adding custom CSS variables (for developers extending the theme):

1. Go to Online Store → Themes → Edit code
2. Open assets/base.css (Dawn) or equivalent
3. Add your custom variables to the :root block, referencing the theme's settings variables:

:root {
  --color-button: {{ settings.color_button.red }}, {{ settings.color_button.green }}, {{ settings.color_button.blue }};
  --font-body-family: {{ settings.type_body_font.family }}, sans-serif;
}

4. In your section/component Liquid files, use var(--color-button) to reference the merchant-controlled setting

---

WooCommerce

Block themes with theme.json (WordPress 5.9+):

If you're building a new store with a block theme (like Storefront Blocks or a custom block theme):

1. Open theme.json in your theme root
2. Add your design tokens to the settings.color.palette and settings.typography sections:

{
  "settings": {
    "color": {
      "palette": [
        { "slug": "brand-primary", "color": "#2563eb", "name": "Brand Primary" },
        { "slug": "brand-secondary", "color": "#3b82f6", "name": "Brand Secondary" }
      ]
    },
    "custom": {
      "spacing": { "xs": "0.5rem", "sm": "1rem", "md": "1.5rem" }
    }
  }
}

3. WordPress automatically exposes these in the Global Styles panel and generates CSS custom properties like --wp--preset--color--brand-primary

Classic themes — CSS variables in Additional CSS:

1. Go to Appearance → Customize → Additional CSS
2. Define your brand variables:

:root {
  --color-primary: #2563eb;
  --color-price-sale: #dc2626;
  --font-size-base: 1rem;
  --border-radius-button: 0.375rem;
}

3. Use these variables in your child theme's CSS instead of hard-coded values

---

BigCommerce

Cornerstone theme variables (SCSS-based):

1. Go to Storefront → My Themes → Edit Theme Files (requires a copy of the theme)
2. Open assets/scss/settings/global/ — Cornerstone organizes variables by category (color, typography, spacing)
3. Modify _color.scss to update the brand color palette
4. Open config.json in the theme root — this maps Theme Editor controls to SCSS variables:

{
  "settings": {
    "color-primary": "#2563eb",
    "font-size-root": "16px",
    "button-radius": "4px"
  }
}

5. In Storefront → My Themes → Customize, the Theme Editor reflects these settings for merchant configuration

---

Custom / Headless

Three-tier CSS custom properties system:

/* 1. Global tokens — the complete palette (never used directly in components) */
:root {
  --blue-600: #2563eb;
  --blue-500: #3b82f6;
  --red-500: #ef4444;
  --green-600: #16a34a;
  --gray-50: #f8fafc;
  --gray-900: #0f172a;
  --space-4: 1rem;
  --space-6: 1.5rem;
  --radius-md: 0.375rem;
}

/* 2. Semantic tokens — meaningful aliases (components consume these) */
:root {
  --color-brand-primary: var(--blue-600);
  --color-brand-secondary: var(--blue-500);
  --color-surface: var(--gray-50);
  --color-on-surface: var(--gray-900);
  --color-price: var(--gray-900);
  --color-price-sale: var(--red-500);
  --color-success: var(--green-600);
}

/* 3. Dark mode overrides */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --color-surface: var(--gray-900);
    --color-on-surface: var(--gray-50);
  }
}
[data-theme="dark"] {
  --color-surface: var(--gray-900);
  --color-on-surface: var(--gray-50);
}

/* Components only use semantic tokens */
.btn-primary {
  background: var(--color-brand-primary);
  border-radius: var(--radius-md);
  min-height: 44px;
}
.price--sale { color: var(--color-price-sale); }

Dark mode toggle (stores preference in localStorage):

export function ThemeToggle() {
  const [theme, setTheme] = useState(() => localStorage.getItem('theme') ?? 'system');

  function applyTheme(newTheme) {
    setTheme(newTheme);
    localStorage.setItem('theme', newTheme);
    if (newTheme === 'system') document.documentElement.removeAttribute('data-theme');
    else document.documentElement.setAttribute('data-theme', newTheme);
  }

  return (
    <button onClick={() => applyTheme(theme === 'dark' ? 'light' : 'dark')}
      aria-label={`Switch to ${theme === 'dark' ? 'light' : 'dark'} mode`}>
      {theme === 'dark' ? 'Light mode' : 'Dark mode'}
    </button>
  );
}

Prevent dark mode flash (apply before render):

<!-- In <head>, before any stylesheets -->
<script>
  (function() {
    var theme = localStorage.getItem('theme');
    if (theme === 'dark' || (!theme && matchMedia('(prefers-color-scheme: dark)').matches))
      document.documentElement.setAttribute('data-theme', 'dark');
  })();
</script>

Multi-tenant white-label (inject per-tenant overrides server-side):

// In your server response, inject tenant CSS overrides in <head>
// so they're applied before the page renders (no flash)
const tenantTheme = await getTenantTheme(req.hostname);
const cssOverrides = tenantTheme
  ? `:root { ${Object.entries(tenantTheme)
      .map(([k, v]) => `--${k}: ${sanitizeCssValue(v)};`)
      .join(' ')} }`
  : '';

// Sanitize to allow only safe CSS value patterns
function sanitizeCssValue(value) {
  if (/^#[0-9a-fA-F]{3,8}$/.test(value)) return value; // hex color
  if (/^\d+(\.\d+)?(px|rem|em|%)$/.test(value)) return value; // length
  if (/^[a-zA-Z0-9\s,'"]+$/.test(value)) return value; // font names
  return ''; // reject everything else (prevents CSS injection)
}

Step 3: Build a token reference for your team

Regardless of platform, document your tokens so designers and developers stay in sync:

• Shopify: The Theme Editor serves as the live token reference — share the Customize URL with your design team
• WooCommerce: Document the CSS variable names in a Storybook instance or a simple HTML reference page
• BigCommerce: Cornerstone's config.json documents available settings; add comments to SCSS files
• Custom: Use Style Dictionary to generate a static token documentation page, or document in Storybook

Best Practices

• Never hard-code colors in component CSS — always use semantic tokens; a rebrand that requires global find-replace of #2563eb is avoidable
• Keep semantic token names meaning-based — --color-brand-primary not --color-blue-600; the hex value will change but the meaning stays
• Test dark mode with real devices — macOS/iOS and Windows have different default dark mode behaviors; test both
• Validate contrast ratios — after setting brand colors, verify WCAG contrast ratios (4.5:1 for body text) using WebAIM Contrast Checker
• Sanitize white-label CSS injections — only allow hex colors, rem/px lengths, and font names; reject arbitrary strings to prevent CSS injection attacks

Common Pitfalls

Problem	Solution
Dark mode causes flash of unstyled content	Apply data-theme attribute synchronously in a <head> script before stylesheets load
Tenant theme overrides not applied on first render	Inject tenant CSS as inline <style> tag server-side; do not apply in useEffect
Design tokens out of sync between Figma and code	Use Tokens Studio for Figma plugin to export directly to your CSS variable / theme.json files
White-label CSS enables XSS	Sanitize tenant token values to only allow valid CSS color, length, and font-family patterns
Rebranding requires changing many files	If you find yourself replacing colors in multiple component files, you skipped the semantic token layer — refactor to semantic tokens first

Related Skills

• @responsive-storefront
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