How do I change the button color for a Dynamic Textbox?

Just trying to change the color of the button. Cannot figure out the correct css code for it. 

You can use this custom CSS to all your dynamic textbox widget.

#addVar{
background-color: red !important;
}

Please give it a try and let us know if you need further assistance.

Thanks so much for your help, this did work and I was able to adjust with hex color code as well. :)