twitter widget background

have managed to edit embedded code from twitter widget, to show data-chrome: transparent to make background at least clear which shows the page colour behind, but if you wanted to edit the background of the twitter widget to a colour (but not the standard white), then how is it done? I’ve searched masses on the web and no-one says how. One person suggested without exact details to just edit the transparent colour to whatever colour you want, well this doesn’t work, so how? Surely there ought to be a way of altering the data-chrome: transparent bit to a hex colour code, any ideas?

I can make the colour change on firefox preview, but I can’t find where this code lives, in an iframe etc….within the wordpress files. I do not use FTP so editing only via css child theme is my route. But no changes work as yet.