Unity error on highlighting buttons

HI, I’m new to Unity, and I’m trying to create a survey questionnaire inside my game.
I have two buttons, the same height and length, and are close to each other. I want them to turn yellow when highlighted, and I specified this in unity editor. It works well, but when I press one of those buttons and position the cursor at the top of “the same button” (not the one close to it), it doesn’t turn yellow. Only If I start checking some checkboxes on top of it, then it starts working again. could be an error of focus, I don’t know. how can I overcome this error? Here’s a .gif illustrating the error, I’m only using regular UI stuff, like Buttons and checkboxes

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