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Give this a shot:

#wpsp-12540 .wp-show-posts-image {
    margin-bottom: 0;
    width: 50%;
    margin-right: 0;
}

#wpsp-12540 .wp-show-posts-inner {
    align-items: center;
    display: flex;
    flex-wrap: wrap;
}

#wpsp-12540 header.wp-show-posts-entry-header {
    width: 50%;
    box-sizing: border-box;
}

As for the validation, you can try a plugin like Autoptimize which should bundle all of the CSS/JS on the page.