The corresponding SquareLine documentation states that you can set the active tab button’s style in ‘Checked’ mode.
So select the whole TabView for editing, then in Inspector Panel in ‘STYLE SETTINGS’ modify state to ‘CHECKED’, then in ‘STYLE (BUTTONS ITEMS)’ make the style-changes you wish to see on the focused selector/title-button.
As mentioned by you its not yet worked. if i change the colour all buttons colour are getting changed instead of focus/selector colour. Could you share me a detailed visual steps or Video. Since i’m new user not able attach my video. But for sure i have tried you several times but not yet work as i’m expected