user.css

#txt2img_gallery, #img2img_gallery{
    /* Output height */
    height: 680px;
}

#txt2img_results, #img2img_results{
    /* Output width */
    min-width: 50%;
}

#txt2img_gallery > .grid-wrap, #txt2img_gallery > .preview,
#img2img_gallery > .grid-wrap, #img2img_gallery > .preview{
    max-height: none;
}