How to make a Widget Borderless?

Hello,
I don’t know css but what I want I think would be simple for someone who does.
My WordPress theme (Parament) creates borders for Widgets. So anything I place in a widget (such as in image) will be framed by a border.
Can I define a class that will display no border for a particular widget?

I have installed ‘Widget CSS Classes’ and I have created a class called ‘Borderless Widget’. But I have no idea how to actually code this item.

What CSS code is needed to remove the border from whatever Widget I apply this Class to? And where do I paste this code?

I’m sorry to ask for so much! 😛 But TIA!

http://ww.wp.xz.cn/extend/plugins/widget-css-classes/