Lets be honest: Android's default volume panel is pretty boring. It does its job, but it's super basic, and many of the options to enhance its functionality are root-only, which excludes a large number of Android users. Enter Noyze Volume Panel, a customizable replacement that doesn't require root access (or any other modifications) and works well.
Once installed, Noyze requires activation in Accessibility settings, but after that it's basically on autopilot. The basic version of the app includes a couple of simple themes, like a minimal status bar slider and extended controls, but for those looking for a bit more use out of the app there's also a pro version for $1.58 USD.
Noyze does a bit more than just enhance the volume panel, however. It can also assign apps to volume up/down long-presses, as well as disable volume buttons altogether (for devices that may have broken buttons) and a few other simple, but related tweaks.
Overall it's a very cool app and provides a good amount of utility for a small price tag.