The biggest problem of Android is the updates, which are quite slow, or not even a thing. You won't get the Pie update soon unless you are using a Pixel phone, or an Essential PH-1. Thanks to the developer Trey Dev, you can get a glimpse of Android 9 on your device right now. He developed an app called Power Shade, which mimics the Quick settings and Notification shade UI and runs on pre-9.0 devices going back to 5.0.
Install Power Shade
The first thing you have to do is installing the Power Shade app. If you are curious and want to test the beta, you can join the Power Shade | Material Telegram group and test it out. Also, you can report there if you encounter any bugs or glitches. The app is free but has a pro version which unlocks some additional customization features, but it isn't necessary.
Enable Power Shade
After installing the app, you will need to swipe right the arrow on the top where it says 'Not running'. This will get to you to a page in which you will be guided to enable the necessary permissions for the application to function properly. If you have given the access needed, then you are good to go.
Customize Power Shade (If you choose to)
There are four options in the settings of the app, with which you can tinker:
Trigger - You can access the Notification shade by swiping on the left or right edge of your device. It's useful for phones with taller screens with ratios like 18:9, 18.5:9, 18.7:9, 19:9 and so on.
Colors - You can change almost everything, but modifying the transparency level requires the pro version.
Layout - Here you will find many pro options like changing the grid size, plus the number of the tiles shown at the top and more.
Extras - The Extras page is all about further personalizing the appearance of the panel by adding a custom background and profile images, a carrier name and changing the font too as free features.
Now, it is time to use it
So, my setup using the free version is all about a combination between black(#000000) and Deep Teal 500 (#009688), with black panel and notifications background and teal accents. I hope you like it.
Please, tell us what are your thoughts about Power Shade, and if you want to support the developer, get the pro version.