What is the HEX code for Transparent color?

There is no such thing; transparency is done via another channel.

For me it worked using the format #AARRGGBB so the one working for me was #1C00ff00. Give it a try, because I have seen it working for some and not working for someone else. I am using it in CSS.

It depends on the format, some systems require RRGGBB, which doesn't include alpha.

Some have their format as AARRGGBB, so your provided color would be 05FF00FF.

Conversely, some have their format as RRGGBBAA, thus your provided color would be FF00FF05.

You can also use #00000000

I found that after using #1C00ff00 which also worked