Before the rise of Substratum, there was the CyanogenMod Theme Engine (CMTE). Introduced all the way back with CyanogenMod 9 (based on Android Ice Cream Sandwich), it added system-wide theme capabilities to CyanogenMod builds. With the release of CyanogenMod 14 (which later became LineageOS), CMTE was nowhere to be found. Meanwhile many other popular custom...