How do you show “only image” posts?

To show “only image” posts in Showcase category. I have used the following code:

.format-image.has-thumbnail .item-main, body.masonry-relayout .format-image.has-thumbnail .item-main {
    display: none;
}

.format-image.has-thumbnail:hover .item-thumbnail {
    margin: -20px -20px 15px;
}

.single .format-image .item-title, .single .format-image .meta-top, .single .format-image .meta-bottom, .format-image:hover .item-main, .format-image:hover .item-title, .format-image:hover .meta-top, .format-image:hover .meta-bottom {
    display: block;
}

Following your instruction, I pasted the above code into style.css. However, nothing happens. Please advice. Thanks.

@Nam Do !

May you mistake? The Showcase page only allows displaying the images. If you want to have this format for other pages, please let me know the page you want to customize, we will give to you our solution.

Thanks and cheers!