You can close them by pressing the Esc key.
There’s also a small x in the upper right corner, and if there’s more than one displayed at a time, there should also be a prominent button allowing you to dismiss all of them.
Note, it does take a moment until the notification has identified whether the issue has already been reported. If it can’t find it, please do consider opening a new issue for it, using the button provided (unless you can fix it yourself).
I’m a little colorblind. I can just barely see that x in the screenshot on 1 of my 5 monitors.
You can inspect its class using Chromium’s Inspector and style it using CSS, so that you can choose the color you see best.