Making the cursor blink

[jatin-47]

It looks good when the cursor blinks.

[hrushikeshrv]

I agree. Currently the cursor is just a | character rendered by MathJax, and I'm not sure if we can/should be able to apply animations to it. I have noticed that the | character rendered by MathJax has a class of mjx-c7C applied, so maybe we could add an animation to that class through mjxgui.css, but I'm not sure if that will work and if it will be stable. But you can try it out and we will see how it turns out 👍🏻