It looks like the padding in the cards is coming from this:
.canvas-node-content.markdown-embed > .markdown-embed-content > .markdown-preview-view {
padding: 0 var(--size-4-6);
}
so you could try adjusting that a bit. e.g.
.canvas-node-content.markdown-embed > .markdown-embed-content > .markdown-preview-view {
padding: 0 10px;
}
There’s still a bit off to the right, I suppose for the scrollbar, but maybe you can make this work.