How can I Change the Color of Post-thumbnail from white to black?

Hi there,

difficult as that method is using an Embed, so what you see is an iFrame, which loads its own stylesheets in the iframe. And they cannot be directly overwritten with your normal CSS stylesheets.

Instead why not us the GenerateBlocks 1.5 Query Loop Block to display the posts ?

https://docs.generateblocks.com/article/query-loop-overview/

And we just added some patterns to our library that you can use to get started:

https://generateblocks.com/library/