thumbnail size

Accordking to this

“I’m using the Thumbnails display. How can I change the thumbnail size?
The default YARPP thumbnail size is 120px by 120px. The thumbnail size can be specified programmatically by adding add_image_size( ‘yarpp-thumbnail’, $width, $height, true ); to your theme’s functions.php file with appropriate width and height variables. In the future I may add some UI to the settings to also set this. Feedback is requested on whether this is a good idea.” This does not work in my functions.php file – it causes no display of the website at all.

Am trying this in CSS – .yarpp-thumbnail {height: 150px; width:auto; !important;} – but does not work either. How do I get my thumbs to be something like 150×225 px?

Thanks.

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