A sequence of square icons shows a single straight line passing through the center of each square, rotating clockwise. In Step 1, the line is vertical. In Step 2, the line is diagonal from the top-left corner to the bottom-right corner. In Step 3, the line is horizontal. In Step 4, the line is diagonal from the bottom-left corner to the top-right corner. Following this continuous rotational pattern, what is the orientation of the line in Step 7?