I found Liquidbounce's original GUI

[END3R1355]

Minecraft - 1.9 LiquidBounce Client 1.9 Minecraft Hacked Client - WiZARD HAX – 02:04
— WiZARDHAX.com

Back in 2016, most clients made that year used darkstorm652's GUI API https://github.com/DarkStorm652/Minecraft-GUI-API

Liquidbounce was one of the clients that used it but later on replaced with another one

Jigsaw also used the Darkstorm API (still in the src code)

[chanisthegreat]

@e-nder1355 wizardhax