⠄⠄⣿⣿⣿⣿⠘⡿⢛⣿⣿⣿⣿⣿⣧⢻⣿⣿⠃⠸⣿⣿⣿⠄⠄⠄⠄⠄
⠄⠄⣿⣿⣿⣿⢀⠼⣛⣛⣭⢭⣟⣛⣛⣛⠿⠿⢆⡠⢿⣿⣿⠄⠄⠄⠄⠄
⠄⠄⠸⣿⣿⢣⢶⣟⣿⣖⣿⣷⣻⣮⡿⣽⣿⣻⣖⣶⣤⣭⡉⠄⠄⠄⠄⠄
⠄⠄⠄⢹⠣⣛⣣⣭⣭⣭⣁⡛⠻⢽⣿⣿⣿⣿⢻⣿⣿⣿⣽⡧⡄⠄⠄⠄
⠄⠄⠄⠄⣼⣿⣿⣿⣿⣿⣿⣿⣿⣶⣌⡛⢿⣽⢘⣿⣷⣿⡻⠏⣛⣀⠄⠄
⠄⠄⠄⣼⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣦⠙⡅⣿⠚⣡⣴⣿⣿⣿⡆⠄
⠄⠄⣰⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣷⠄⣱⣾⣿⣿⣿⣿⣿⣿⠄
⠄⢀⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⢸⣿⣿⣿⣿⣿⣿⣿⣿⠄
⠄⣸⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⡿⠣⣿⣿⣿⣿⣿⣿⣿⣿⣿⠄
⠄⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⠿⠛⠑⣿⣮⣝⣛⠿⠿⣿⣿⣿⣿⠄
⢠⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣶⠄⠄⠄⠄⣿⣿⣿⣿⣿⣿⣿⣿⣿⡟⠄

:host-context()

The :host-context() CSS pseudo-class function selects the shadow host of the shadow DOM containing the CSS it is used inside (so you can select a custom element from inside its shadow DOM) — but only if the selector given as the function's parameter matches the shadow host's ancestor(s) in the place it sits inside the DOM hierarchy.
:host-context() css reference