<blockquote>
I have changed the css for the “live demo” button in /purity3/css/bootstrap.css a
</blockquote>
It is not recommended to edit that file since it will be overridden when you upgrade the template or compile Less to CSS.
<blockquote>
but as I said, the changes aren’t taking effect even with the !important bit
</blockquote>
Instead, please create a new file “custom.css” in folder “templates/purity3/css” (if it does not exists) then insert your custom css code into this file.
If it still does not help, pls PM me admin, url and ftp access your site, I’ll investigate further and help you out.