Why It Matters
Google indexes and ranks the mobile version of every website (mobile-first indexing), so content or usability problems on mobile affect your rankings everywhere. A non-responsive layout also drives mobile visitors away before they convert.
Viewport Meta Tag: Add <meta name="viewport" content="width=device-width, initial-scale=1.0"> inside your HTML head section.
Fluid CSS Layouts: Use modern CSS Grid and Flexbox with relative sizing units (rem, %, vw) to ensure elements adjust smoothly across device widths.
Sufficient Touch Target Sizes: Ensure interactive elements (buttons, links) are at least 48x48 pixels with ample spacing to prevent accidental taps.
Legible Mobile Typography: Maintain a base font size of at least 16px. Using 16px or larger on form fields also stops iPhones from zooming in when someone taps a field.