We’ve all been asynchronously loading JavaScript for many years. It helps speed up page loading and perceived page loading.

It hadn’t even occurred to me to asynchronously load CSS to speed up (and give even more perceptively speed) for that initial load and render.
Like most things in the front end world, there are multiple ways to do it, but the article linked below shows an easy way to do it.

Source: Filament Group – The Simplest Way to Load CSS Asynchronously