Why is :box not getting the current background color?. It doesn't even work if I setq a variable with the color hardcoded, but if I set the hex color as a literal it works perfectly. If I evaluate manually the sexp (face-background 'default) it returns the right color #1E1C31 ( a dark color, but if you notice on the screenshot is setting a bright color ).

 (set-face-attribute 'tab-bar-tab-inactive nil
                        :family "Cascadia"
                        :foreground (face-foreground 'default)
                        :background (face-background 'default)
                        :height 1.3
                        :slant 'italic
                        :box '(:line-width 9 :color (face-background 'default))
                        )