TextBlock Run Background Span Whole Line

Question

Is it possible to make a run span the entire width of a TextBlock so the background looks natural and not just on the text of the run?

Current Result:

Expected Result:

Another issue with the first image is that there are (unwanted) white lines between certain Runs (in this case "test" and "1"). My current code is:

Run r = new Run("You: " + SendMessageBox.Text + "\n");
r.Background = Brushes.LightBlue;
ChatHistory.Inlines.Add(r);

Answer 1

Is it possible to make a run span the entire width of a TextBlock so the background looks natural and not just on the text of the run?

No, you should add another TextBlock element for each line:

TextBlock t = new TextBlock() { Text = "You: " + SendMessageBox.Text };
t.Background = Brushes.LightBlue;
ChatHistory.Children.Add(t);

ChatHistory could for example be a StackPanel: