Sorry, but it won’t look fine using CSS code only, without additional customization (additional customization is outside the scope of our support).
The fixed header is generated automatically by the script. That’s why if you want to change its content you need to edit script https://prnt.sc/hp5ms5 (xstore/js/etheme.js, xstore/js/etheme.min.js). Do changes via child theme.
If you need any help with additional customization, please, submit customization request here. Unfortunately, theme support covers only questions related to existing theme options and minor CSS customization.