The Yet Another Related Posts Plugin (YARPP) is very popular plugin for WordPress to display related posts in posts and feeds. Upon activating the YARPP plugin, it will automatically add and load several CSS stylesheet calls, namely related.css in footer and widget.css in header (with <head> and </head>.

The YARPP CSS stylesheets are not necessary if you’re using custom template with own styling defined in other CSS stylesheets, or if the website doesn’t load related posts on the frontend.

To disable and prevent the loading of YARPP CSS stylesheets in the header and footer, add the following code into the active theme’s functions.php file:

add_action( 'wp_print_styles', 'tj_deregister_yarpp_header_styles' );
function tj_deregister_yarpp_header_styles() {
   // Next line is required if the related.css is loaded in header when disabled in footer.

add_action( 'wp_footer', 'tj_deregister_yarpp_footer_styles' );
function tj_deregister_yarpp_footer_styles() {

As per comment in the code, “wp_deregister_style(‘yarppRelatedCss’);” can be commented out if related.css is not loaded, or does not face the issue where it’s been loaded in header when prevented from loading in footer.