If you are hosting your blog on WordPress.com then you are not able to add these type of buttons in the Vantage theme. You can however using your hosting account.
Open up File Manager and open up the folder wp-content and navigate to the vantage folder
Download the file called header.php and rename the downloaded file header_home.php
Upload this file to the Vantage theme. You now have two different header php files
And the following code to header_home.php after the line ( 'vantage_after_masthead' ); ?> and save
the css code is available here https://siteorigin.com/wp-content/plugins/so-theme-widgets/widgets/plugin-header/assets/css/style.css?ver=1.5.6
In this file delete the line header() and add include ‘header_home.php’