Hi Nikos, and sorry about the issues!
I tried it out, and it's working.
Did you check into browser extensions or settings ? It's less likely as you tried it in two browsers, but still possible; as many have similar settings/extensions across different browsers.
Please post a screenshot of your submission failing, and make it of your entire browser. You can use the Toggle Navigation button (or Table of Contents button) at the top of the challenge to move forward, too, so you're not stuck.