Replace the Upgrade button with a custom image

Hi all,

Hope someone already managed to do this. SO I would like to change the CTA on the top admin bar with a custom image. Looking at the CSS, something needs to be changed to the following ids
#wpadminbar li#wp-admin-bar-pro-site
#wpadminbar li#wp-admin-bar-pro-site a
#wpadminbar li#wp-admin-bar-pro-site a span

I don't want to modify the css of the plugin, just to overwrite it with css added into the Branding plugin.

And it's the #wpadminbar li#wp-admin-bar-pro-site a span that has a lot of !important, which makes it difficult to overwrite

background-image: -moz-linear-gradient(bottom, #3b85ad, #419ece) !important;
background-image: -ms-linear-gradient(bottom, #3b85ad, #419ece) !important;
background-image: -webkit-gradient(linear, left bottom, left top, from(#3b85ad), to(#419ece)) !important;
background-image: -webkit-linear-gradient(bottom, #419ece, #3b85ad) !important;
background-image: linear-gradient(bottom, #3b85ad, #419ece) !important;

Thank you!

Best,
M