Tangentially to the topic, I mention mainly for the benefit of new members that by default, Windows 10 includes transparency (Aero) effects in the Start Menu, Desktop Taskbar, and Action Center. But it reduces contrast and consumes a little bit of resources if your graphics card is weak. If you feel like me that you're better off without it, you can easily disable it thru Settings > Personalization > Colors
Classic Shell has a percentage value for Taskbar Opacity. To change this value, first check the box labeled Customize Taskbar and then choose Transparent.