Unable to set gtk Calendar button color

Platform
, ,
1

I wanna change the header button color of the calendar widget-

image
image1130×644 106 KB

rust code-
let gtk_calendar = GtkCalendar::new();
gtk_calendar.set_css_classes(&[“calendar”, “calendar-gtk-calendar”]);

css-
.calendar-gtk-calendar {
min-width: 400px;
min-height: 200px;
border-radius: 10px;
background-color: @primary-color;
}
.calendar-gtk-calendar * {
color: @bg-color-no-transparent;
border-color: @bg-color-no-transparent;
}
.calendar-gtk-calendar header button {
all: unset;
background-image: none;
background-color: red;
background: red;
color: red;
border: none;
}

anyone know how to?