How to add a shadow box behind the title in poster image block

Hi there,

I'm currently building a site in the square-space trial so I don't think I can share my url. However, I basically looking to add a grey background block, with an opacity of around 80% to my title's on poster image blocks to make the text more legible. A bit like the inline version, expect I want it permanent, not only on hover and in the centre. I can't work out the code to do this, can anyone help?! Thanks in advance.

You can try this Design -> Custom Css

.sqs-block-image .design-layout-poster .image-card {
  background: rgb(128 128 128 / 0.8);
  padding: 1em;
}

45 minutes ago, bangank36 said:

You can try this Design -> Custom Css

.sqs-block-image .design-layout-poster .image-card {
  background: rgb(128 128 128 / 0.8);
  padding: 1em;
}

 

Thank you! That looks great but I get this message I'm afraid I'm unsure what it means: Is there a hex code version? Thanks! 

error evaluating function `rgb`: color functions take numbers as parameters

Sorry try this

#808080cc