Filter question

How do I add a brightness filter to my profile? I saw one on a layout but I don't know how to do it on my own if that makes sense. I only know how to add an overlay. The brightness filter I saw looked like this:

}

img {    

    filter: brightness(1.75);

}

    but when I put it into my layout it doesn't work. Does anyone have a code or anything to help me add this to my profile?