Full-Stack Engineer Career Path - Code Editor is nor editable, not responding

I cannot enter any code in the code editor workspace. Here is the location:

JavaScript Syntax Part 1 → Introduction to Programming with JavaScript → Learn JavaScript Syntax: Introduction → Introduction to JavaScript → Arithmetic Operators

app.js file is not editable and unless I complete the required task I cannot move to “Next” section.

Hoping for any help.

Thank you.