When you press the panel's close button, so will the panel go away. What did you press to do that? It will be something like Alt+F4 or Alt+Z. Very easy to remember. But for the content of the dialogs, that differ per text engine, just click on the content you want to change (or leave empty).
Now on the Preview tab go to the Shape tab and select Gradient. Suddenly the preview is shown in the preview window. But did you ever noticed that at the round configuration, the Preview tab is not selected? Well, this is because it does not preview a gradient. That is why you need to switch to the gradient tab because there the X, Y, Shape and Radial gradient settings can be seen, but not in the Preview tab. Let's go to gradients:
First, the gradient should have an angle. Drag the angle slider to a direction you want to preview. Drag the slider again to the other direction and this stops the preview. Now quickly set the Stop position to green and try the preview. It will show this red dot while the line continues towards the green position. It is the position where the gradient dies. Drag the green (or blue) position, and it will stop. You can also adjust the color-stop positions for each color-stop via the color-dropdown.
Now, the gradient is set. To make it a ring gradient, go the shape tab and select Radial. Pick a starting point X, Y and shape, and the preview will show you the various lines coming from that point. Also see the gradient angle in the preview window. Now, let's set two of the color-stops, so it looks like a ring gradient. d2c66b5586