For light, I’m in my warm library… Terminal is just translucent enough to pick up background hints.
To get guayadeque in the right ballpark I discovered my new favourite light GTK theme which is breeze-solarized-light which goes along with my ‘card’ color theme (easily found and downloaded in the KDE dialogue).
For dark, I’m not fussy - as long as it’s gentler shades of grey - oh, and with either light or dark it must be the ‘breeze-Chameleon’ which take their colour from the theme as you see in Dolphin there. If I put on my ‘marble’ colours you’ll see this: