// These two below values/ratio would be calculated dynamically,

public string firstColValue = "3*";
public string secondColValue = "7*";

<Frame CornerRadius="8" Grid.Row="0" HorizontalOptions="FillAndExpand" HeightRequest="8">
<Grid HorizontalOptions="FillAndExpand">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="{Binding firstColValue}">
            </ColumnDefinition>
            <ColumnDefinition Width="{Binding secondColValue}">
            </ColumnDefinition>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="8">
            </RowDefinition>
        </Grid.RowDefinitions>

            <Label Grid.Row="0" Grid.Column="0" HeightRequest="8" HorizontalOptions="FillAndExpand" BackgroundColor="Lime"></Label>
            <Label Grid.Row="0" Grid.Column="1" HeightRequest="8" HorizontalOptions="FillAndExpand" BackgroundColor="Blue"></Label>

    </Grid>
</Frame>