Your website should be mobile first.
This means, you should design for a mobile phone before you design your desktop version.
Mobile phones have a smaller viewport and can often result in a skimmed version of your main page.
It is likely that you may be in a handful of industries where users use your desktop site more than mobile.
You would notice that your mobile traffic continues to increase and will do so in the future.
Even Google has switched to a mobile crawler in the past few years.
You can confirm this via the Google search console.
Check the viewport meta tag
The viewport meta tag tells the browser how to scale a page to fit on a mobile device. Without this tag, your pages will not be responsive and will not look good on mobile devices.
Check the width of your content
Make sure that your content is not too wide for mobile devices. If your content is too wide, it will require users to scroll horizontally to see all of the information, which is not a good user experience.
Check the font size
Make sure that your font size is large enough to be legible on mobile devices. Small font sizes can be difficult to read on small screens.
Check for touch-friendly elements
Make sure that your buttons and links are large enough to be easily clicked on mobile devices. Small buttons and links can be difficult to click on a touchscreen.
Check your images
Make sure that your images are optimized for mobile devices. Large images can take a long time to load on mobile networks.
Check your videos
Make sure that your videos are optimized for mobile devices. Videos that are not optimized for mobile devices can be slow to load and may not play properly on some devices.
Test, test, test!
The best way to ensure that your site is responsive is to test it on as many different devices as possible. Try testing on different smartphones, tablets, and desktop browsers to get a comprehensive understanding of how your site looks and functions on different screen sizes