I've applied it in the Styles property - both by setting the Alpha in Color picker and also via the extra .css box.
It just shows up as a solid grey?
You can see the values on the right.
Make sure the Emded HTML is this;
I can replicate your problem by replacing 'https://twitter.com/{$id}/status/{$id}' with 'https://twitter.com/*/status/{$id}'