Responsive or mobile-friendly themes
A responsive theme's layout adjusts to your device's screen size. It provides an optimal viewing experience, easy reading, and accessible navigation on mobile phones, tablets, laptop and desktop computers.
You can see a list of responsive themes in the Shopify Theme Store.
How to check if a theme is responsive
Resize your browser window to make it smaller. If the layout of a theme changes based on the size of the browser window, then the theme is responsive. Themes that are not responsive will not adapt to smaller window sizes.