some minor improvements for dark mode UI

fieldset span.text-gray-500, .gr-block.gr-box span.text-gray-500,  label.block span{

    position: absolute;

    top: -0.5em;

    top: -0.7em;

    line-height: 1.2em;

    padding: 0;

    margin: 0 0.5em;

    background-color: white;

    box-shadow: 0 0 5px 5px white;

    box-shadow:  6px 0 6px 0px white, -6px 0 6px 0px white;

    z-index: 300;

}

.dark fieldset span.text-gray-500, .dark .gr-block.gr-box span.text-gray-500, .dark label.block span{

    background-color: rgb(31, 41, 55);

    box-shadow: 0 0 5px 5px rgb(31, 41, 55);

    box-shadow: 6px 0 6px 0px rgb(31, 41, 55), -6px 0 6px 0px rgb(31, 41, 55);

}

#txt2img_column_batch, #img2img_column_batch{