Embracing Mobile‑First Design

Note: This article was originally published on September 18, 2017. Some information may be outdated.

Google moved to mobile‑first indexing in 2017, using the mobile version of pages for ranking and crawling. This shift echoed traffic trends showing mobile visits overtaking desktop early that year.

Designing mobile‑first means writing base CSS for narrow screens first, then layering on styles for larger breakpoints. It results in smaller payloads and faster first paints on phones.

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Step‑by‑step example

Base (mobile) styles

/* styles.css */
body {
  font-family: system-ui, sans-serif;
  margin: 0;
}

.card {
  padding: 1rem;
  border-bottom: 1px solid #ddd;
}

Enhance for tablets

@media (min-width: 600px) {
  .cards {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
  }
  .card {
    flex: 1 1 calc(50% - 1rem);
    border: 1px solid #ddd;
  }
}

Desktop upgrade

@media (min-width: 960px) {
  .card {
    flex: 1 1 calc(33.333% - 1rem);
  }
}

Media queries add complexity after the core experience works, keeping small‑screen CSS lean.

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Practical checklist

• Content first: prioritise copy and actions most important on phones.
• Fluid images: set img { max-width: 100%; height: auto; }.
• Touch targets: minimum 48 × 48 px tap area.
• Font sizes: avoid fixed pixel fonts; use rem or viewport units.
• Test real devices: DevTools emulation catches layout, not touch ergonomics.
• Performance budgets: keep initial CSS under 14 KB uncompressed to fit the first TCP round‑trip.

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SEO and analytics reminders

Google’s crawler evaluates mobile HTML for ranking, so parity between mobile and desktop markup is crucial. Check Search Console for the “Mobile‑first indexing enabled” flag. Use analytics segments to confirm that mobile now dominates sessions on most sites.

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Mobile‑first design aligns code weight with user reality: phones lead traffic, and search engines judge mobile output first. Starting small and enhancing upward keeps experiences fast and inclusive.

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Originally published at letanure.dev