Changin the width of the scrollbar (not as easy as you think)

I have an issue with the scrollbar width. One character width is too small on my 200 columns terminal, almost invisible.
So I want to change the ScrollbarMargin class to make the width configurable.
But turns out it is not easy at all. I made those simple changes to bring the width to 3 chars:

class ScrollbarMargin(Margin):
    """
    Margin displaying a scrollbar.

    :param display_arrows: Display scroll up/down arrows.
    """

    def __init__(
        self,
        display_arrows: FilterOrBool = False,
        up_arrow_symbol: str = "^",
        down_arrow_symbol: str = "v",
    ) -> None:
        self.display_arrows = to_filter(display_arrows)
        self.up_arrow_symbol = up_arrow_symbol
        self.down_arrow_symbol = down_arrow_symbol
        self.bar_width = 3


    def set_width(self, new_width):
        #TODO 
    
    def get_width(self, get_ui_content: Callable[[], UIContent]) -> int:
        return self.bar_width

    def create_margin(
        self, window_render_info: WindowRenderInfo, width: int, height: int
    ) -> StyleAndTextTuples:
        content_height = window_render_info.content_height
        window_height = window_render_info.window_height
        display_arrows = self.display_arrows()

        if display_arrows:
            window_height -= 2

        try:
            fraction_visible = len(window_render_info.displayed_lines) / float(
                content_height
            )
            fraction_above = window_render_info.vertical_scroll / float(content_height)

            scrollbar_height = int(
                min(window_height, max(1, window_height * fraction_visible))
            )
            scrollbar_top = int(window_height * fraction_above)
        except ZeroDivisionError:
            return []
        else:

            def is_scroll_button(row: int) -> bool:
                "True if we should display a button on this row."
                return scrollbar_top <= row <= scrollbar_top + scrollbar_height

            # Up arrow.
            result: StyleAndTextTuples = []
            if display_arrows:
                result.extend(
                    [
                        ("class:scrollbar.arrow", self.up_arrow_symbol*self.bar_width),
                        ("class:scrollbar", "\n"),
                    ]
                )

            # Scrollbar body.
            scrollbar_background = "class:scrollbar.background"
            scrollbar_background_start = "class:scrollbar.background,scrollbar.start"
            scrollbar_button = "class:scrollbar.button"
            scrollbar_button_end = "class:scrollbar.button,scrollbar.end"

            for i in range(window_height):
                if is_scroll_button(i):
                    if not is_scroll_button(i + 1):
                        # Give the last cell a different style, because we
                        # want to underline this.
                        result.append((scrollbar_button_end, " "*self.bar_width))
                    else:
                        result.append((scrollbar_button, " "*self.bar_width))
                else:
                    if is_scroll_button(i + 1):
                        result.append((scrollbar_background_start, " "*self.bar_width))
                    else:
                        result.append((scrollbar_background, " "*self.bar_width))
                result.append(("", "\n"))

            # Down arrow
            if display_arrows:
                result.append(("class:scrollbar.arrow", self.down_arrow_symbol*self.bar_width))

            return result

Those changes apparently do not affect the rendering of the scrollbar at all. What I'm doing wrong?
Please help! Thanks! 🙏

Start by locating the ScrollbarMargin class and tracing how its get_width and create_margin results are used during terminal rendering. Check why changing bar_width in the shown implementation does not change the displayed margin, then define the configurable-width behavior and verify it with the relevant scrollbar rendering or terminal test if one exists.