If you have a Corporate Marketer account, you can automatically have Content Cards injected into your emails using the Dynamic Content Card content block. This block can be embedded in any email (email reports, autoresponders, campaigns, etc). This is an easy way to automatically inject contextual content into your emails.
When you put this content block into an email, the block can be configured to automatically inject one or more targeted content cards (that arrive within a configured time period before your email is sent and that match a filter criteria) into the email. This makes it very easy to leverage your existing content in your regularly scheduled emails or within workflows. This content block uses the card targeting to ensure that your subscribers get the right content.
The blocks, when injected, will use the styles that you set on the block object
If you are looking to put a separator between each rendered card, you may want to consider adding a bottom border to the block style
You can review the styles of the block with actual content cards by opening the email preview: