Swift does this automatically. Make sure you have it set properly in Settings > Optimization > Styles > Generate Critical CSS.
You can decrease number of HTTP requests if you enable Style & Script merging in Settings > Optimization. If you are using multiple small images (eg icons) you can also enable Media > Images > Inline Small Images feature Swift takes care about expires headers, however please note...
Add the word #sitemap# to the exclude URLs list and then reset the Warmup Table