change colors of a button in a span with data-attr

Hi all!

I've been fiddling with some annoying data-attribure tag. Webmin gives admins the opportunity to adjust the frontend through css but it is with your hands tied behind your back.

I want to change the color of "Send mail" button green with css:

border-color:#1bbf89!important; 
background-color:rgba(27,191,137,.1)!important;

The targeted HTML:

<div class="btn-group end_submits"><button class="btn btn-default ui_submit ui_form_end_submit" type="button">&nbsp;<span data-entry="reply_send">Send Mail&nbsp;</span></button>

I am sure you say: "use 1 of the class attribures like ui_form_end_submit" but those are use for other buttons too and therefor to general.

So i need to target the button tag AND the span data-entry[reply send]