By default, browsers load the assets in a render-blocking way. Modern browsers introduced prefetch and preload which let us specify the priority for a resource without blocking the first render..
This lesson shows you how to use preload and prefetch on an external css.
<link rel="prefetch"
as="style"
onload="this.rel = 'stylesheet'"
href='https://fonts.googleapis.com/css?family=Roboto:400,500|Material+Icons'>
Resource: https://css-tricks.com/prefetching-preloading-prebrowsing/