<?php>
function applyCustomStyles() {
    echo '
    <style>

    /* Change link colour to white */
    #wpbody-content a {
    filter: invert(1) hue-rotate(180deg) saturate(10);
    color: white !important;
    }

    /* Change link colour to yellow */
    #wpbody-content a:hover {
    filter: invert(1) hue-rotate(180deg) saturate(10);
    color: red !important;
    }
    
    /* Styling for primary content area. */
    .block-editor-page .editor-styles-wrapper {
      color: lightgray;
      background: #262626;
    }
    
    /* Base styling adjustments. */
    .wp-admin {
      background-color: #262626;
    }
    
    /* Image display corrections. */
    .wp-admin #wpbody img {
      filter: invert(1) hue-rotate(-180deg);
      background: white;
    }

    /* Enhancements for hyperlink visuals. */
    .block-editor-page .editor-styles-wrapper a {
      filter: invert(0.85) hue-rotate(185deg);
    }
    
    /* Filter reset for specific editor sections. */
    .block-editor-page #wpbody {
      filter: unset;
    }

    /* Adjustments for the main body appearance. */
    .wp-admin #wpbody {
      filter: invert(0.85) hue-rotate(185deg);
    }

    /* Sidebar appearance customization. */
    .block-editor-page .interface-interface-skeleton__sidebar,
    .block-editor-page .interface-interface-skeleton__secondary-sidebar {
      filter: invert(0.85) hue-rotate(185deg);
    }

    /* Configuration for top navigation bar. */
    .block-editor-page .interface-interface-skeleton__header {
      filter: invert(0.85) hue-rotate(185deg);
    }
    
    /* Primary action button styling. */
    .block-editor-page .is-primary {
      color: black !important;
    }
    
    /* Lower section layout adjustments. */
    .block-editor-page .edit-post-layout__metaboxes {
      border-top: 0px;
      background-color: #262626;
    }

    /* Reset various button BG colours */
    .wrap .add-new-h2, .wrap .add-new-h2:active, .wrap .page-title-action, .wrap .page-title-action:active {
    background:#f6f7f700;
    }
    
    </style>';
}
add_action('admin_head', 'applyCustomStyles');