change background color of select box options

[Femeoptob]

I have a drop-down menu in a form on a website that I'd like to change the background of the options to be transparent like the initial selection.I use \[code\]background:rgba(255, 255, 255, 0.2)\[/code\] for that, but how do I apply it to the \[code\]<option>\[/code\]'s.NOTE: This is a Wordpress site and the form is generated by a plugin.