Look in the Realtime Clip FX / Editors, the "MultiShape SpotLight GPU"
You need to customize it.
1- Set the "Inner Shape Blending and Color"
Color Blend: 0.00
2- In the "Outer Shape ..."
Choose a Color Blend value
3- You can also soften the border with the Shape/ Edge Softness
4- Then, you can use the Position and Size tools.