Scrollbar background styling not initially applied (since 0.89)

[davep]

Given this code:

from textual.app import App, ComposeResult
from textual.widgets import OptionList

class BorkedScrollBarBackgroundApp(App[None]):

    CSS = """
    *:focus {
        scrollbar-background: red;
    }
    """

    def compose(self) -> ComposeResult:
        yield OptionList(*(f"This is option {n}" for n in range(1000)))

if __name__ == "__main__":
    BorkedScrollBarBackgroundApp().run()

the expectation would be that the scrollbar's background would be red once the application has run up. This is the case up to Textual v0.88.

Starting with v0.89 the background is the initial styling and only catches up if you do something that causes a refresh (resize the terminal, move he mouse over the scrollbar, that sort of thing).

[TomJGooding]

I thought this might be easy to bisect, but unfortunately it looks like this only worked for the OptionList in v0.88.0.

from textual.app import App, ComposeResult
from textual.widgets import DataTable, Label, ListItem, ListView, OptionList, TextArea


class BorkedScrollBarBackgroundApp(App[None]):
    CSS = """
    *:focus {
        scrollbar-background: red;
    }

    OptionList, ListView, DataTable, TextArea {
        height: 1fr;
    }
    """

    # Try changing the widget that has initial focus
    AUTO_FOCUS = "OptionList"

    def compose(self) -> ComposeResult:
        yield OptionList(*(f"This is option {n}" for n in range(250)))
        yield ListView(*(ListItem(Label(f"This is list item {n}")) for n in range(250)))
        yield DataTable()
        yield TextArea("\n".join((f"This is line {n}") for n in range(250)))

    def on_mount(self) -> None:
        table = self.query_one(DataTable)
        table.add_column("Column")
        for n in range(250):
            table.add_row(f"This is row {n}")


if __name__ == "__main__":
    BorkedScrollBarBackgroundApp().run()