V2.0 will have a "Detailed Log" for Quests, if a player clicks on the Quest it will open a sort of diary for said quest and you can add everything you want to it :)
Viewing post in RPG Maker MZ Plugin: QuestLog comments
You can already change the window skin in the current version with the plugin parameters, no JavaScript needed, just a window skin file to place in the /system folder
Also you can change the RGB tone (from 0 (min) to 255 (max)) always from plugin parameters
I can think about adding the opacity option in v2.0 🙂