Page display speed is also important in terms of the rate at which visitors leave their pages (which would be frustrating if they weren’t displayed immediately) and SEO (which seems to have an impact, though not a major factor), but Google offers services. PageSpeed Insights If you specify a URL, it will make the site faster!It is a wonderful service.
In this article, I picked up one of the techniques introduced there that seems to be more effective in improving page display speed.

put together an image with CSS sprites

CSS sprites are a technique to reduce communication with servers and increase the speed at which images can be displayed. They're particularly useful for things like icons, fine files, etc. here

Delaying JavaScript Loads, Do not Duplicate

For JavaScript that doesn't have to be loaded first, writing the footer in the header instead of writing it backwards will improve display speed, especially since JS for social media-related buttons eats very fast so I recommend loading with footers.
Also, when you load multiple widgets such as Facebook Like button and like box, if you paste the code generated by Facebook directly, it will overlap with JS loading from Facebook.

specify the size of an image, do not change in HTML)

It seems important to specify the size of an image properly with tags, and not to scale or shrink in HTML.

How about it?I hope that this will be a reference to your website creation.