Problem with hovering over outside of element

Hi. It's a simple menu bar. When you hover over each one of left side links in the orange area, the related panel will open in right side of each one, and the hovered link will have a white background with black text color. There's a cool thing when you move your mouse from right panel to the red area (I marked in the attached image), the left side panel still has hover style, by mean, the white background and black text. But I couldn't implementation this cool thing, when I move cursor to the red area, the hover style will disappear. How can I achieve that? Thank you in advance