Web Development

I quite new to web development. I created a simple game which suppose to raise awareness to the RP syndrome (which I suffer from). The simple goal is to find Waldo but the twist is that there is nothing but him on the screen.

I want to add a "flashlight courser effect" meaning that the only visible part of the screen should be the one around the courser (for some fixed or maybe chosen radius). But, I don't want the rest of the screen (the non-visible) to be black but white / blank (as this is in a way the way that I see the world). The other elements (buttons, score and counter) should stay visible always.

Can someone advice me on how can it be done? Ideally there should be two switches (on the corner) one controlling the mode (full visibility vs limited field of vision) and the second one controlling the type of "darkness" (black vs white).

Here is the link to the repo with the current code: https://github.com/menisadi/RPWaldo

Thanks in advance

Update: Thanks everyone!!! I used the SVG idea and added the flashlight effect" (even added a switch to toggle the "flashlight mode" on and off). Working great. Thanks!