How to make background of table cell transparent

You can do it setting the transparency via style right within the table tag:

<table id="Main table" style="background-color:rgba(0, 0, 0, 0);">

The last digit in the rgba function is for transparency. 1 means 100% opaque, while 0 stands for 100% transparent.

It is possible
You just also need to apply the color to 'tbody' element as that's the table body that's been causing our trouble by peeking underneath.
table, tbody, tr, th, td{ background-color: rgba(0, 0, 0, 0.0) !important; }

What is this? :)

background-color: #D8F0DA;

Try

 background: none

And override works only if property is exactly the same.

background doesn't override background-color.

If you want alpha transparency, then use something like this

background: rgba(100, 100, 100, 0.5);