border-styling.css

/*
 * Add a small gap between thumbnails and thumbnails border. This makes
 * thumbnail borders more legible when the thumbnail background is the same
 * color as the border.
 */
@-moz-document domain(donmai.us) {
    .post-preview img {
        /* Play with these to change the border and gap sizes. */
        border-width: 2px !important;
        padding:      2px;

        /*
         * 'dotted' or 'dashed' can be nice choices here, but a little hard to
         * get used to.
         */
        border-style: solid;

        /*
         * Prevent the increased padding from increasing the overall thumbnail
         * size and throwing off the layout.
         */
        box-sizing: border-box;
        max-width:  154px;
        max-height: 154px;
    }

    /*
     * Compensate for the increased padding so that animated/translated
     * thumbnail overlay icons align properly. This takes so many rules because
     * the comments page uses different markup than everywhere else.
     */
    div#c-comments div#a-index div.post-preview div.preview:before,
    div#c-comments div#a-index div.post-preview div.preview a:before,
    div#c-comments div#a-index div.post-preview div.preview a:after,
    div#c-comments div#a-show  div.post-preview div.preview:before,
    div#c-comments div#a-show  div.post-preview div.preview a:before,
    div#c-comments div#a-show  div.post-preview div.preview a:after,
    article.post-preview:before,
    article.post-preview a:before,
    article.post-preview a:after {
        /* margin = padding + border-width from above */
        margin: 4px !important;
    }
}