To use custom modal boxes instead of native `alert()` and `confirm()` calls

[jalaj711]

Rather than using the built-in functions alert() and/or confirm() for user interaction, I think that it would be better if we use custom modal boxes built on HTML/CSS/JS. Doing this will present the following benefits:

• The entire User Experience can be more consistent with the theme of the rest of the website.
• Users on different browsers will still have the same experience, as the UI won't be left on the mercy of the browser.
• We can add more animations over there as well.

[jalaj711]

If the idea sounds good, I can implement this.

[N-Shar-ma]

@jalaj711 Thanks for creating the issue! Custom modals are something that have always been on the todo list, so would indeed love having them!

PS: Please consider a similar way of creating and using modals like in this older project of mine (mainly referring to the use of html template elements a customizable function like showModal) but if you have any alternative ideas, would appreciate you discussing those here too!