Make thumbnails responsive

‘responsive’ in what sense?

can you describe your idea of ‘responsive’ in more detail?

I’d like the images to resize proportionally when the browser window is resized.

I found this tutorial https://www.blissfulinterfaces.com/making-wordpress-images-responsive/

but if I enter this:

function remove_wp_width_height($string){
return preg_replace(‘/\/i’, ”,$string);
}

into my functions.php file, my entire site goes down.