Quite a lot of web browsing is done from a mobile phone so it's important to keep your site lite and fast at least for the next few years until 4G and 5G becomes more established.
CSS (Cascading Style Sheets) contains styling information and the number of style sheets should be kept to a minium, one framework file, an extra font file if required and additional styles could be in line rather than calling up another file.
Code and images should be compressed, with images a first stage 'lossy' compression eliminates some pixel data followed by a 'lossless' that compresses the pixel data.
Code is also compressed in two stages, first 'minified' by removing blank spaces then the file can be Gzipped when sent out from the server.
Run a free website speed test from multiple locations around the globe using real browsers (IE and Chrome) and at real consumer connection speeds. You can run simple tests or perform advanced testing including multi-step transactions, video capture, content blocking and much more. Your results will provide rich diagnostic information including resource loading waterfall charts, Page Speed optimization checks and suggestions for improvements.
Page Speed Insights measures the performance of a page for mobile devices and desktop devices. It fetches the URL twice, once with a mobile user-agent, and once with a desktop-user agent. The PageSpeed Score ranges from 0 to 100 points. A higher score is better and a score of 85 or above indicates that the page is performing well.
For fast app like page loading Google has released a new technology called AMP (Accelerated Mobile Pages), these pages have to follow a very strict coding policy to keep them fast and the pages have to be fairly simple. These pages are also cached or stored by Google for faster delivery on their networks. AMP is best suited for publishers with lots of content they want to deliver at speed without having to develope a range of apps for iOS, Android and Windows.