You can do it using a title overlay with 2 shapes. One with low opacity covering the whole screen and a small green shape placed where the highlight should be.
Apply Chroma Key to the title. When applying Chroma Key to a Title, it hides any elements in the title having the color being keyed out, however it will also hide any element, or part of an element behind the element being keyed out.
I hope this helps.
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