on Dolphin v17.12.3 (included in Kubuntu 18.04 with Plasma v5.12.8 ), where's stored left sidebar sizes?!?

after a fullscreen/windowed switch (from a old low resolution Windows game on Wine) - the left sidebar of Dolphin is was automatic resized (only left sidebar, is was lowersized)

how to restore only left sidebar size from previous backup of config file (/home/user/.config/dolphinrc) ?!?
which string i should extract?!?