GenerateBlocks Accordion Block as Mega Menu in WordPress: https://silvanhagen.com/writing/wordpress-mega-menu-blocks

style.css

.navigation-overlay {
    position: fixed;
    top: 150px;
    left: 0;
    right: 0;
    bottom: 0;
    height: calc(100dvh - 150px);
    max-width: 100% !important;
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    padding-left: calc(50dvw - 600px);
    padding-right: calc(50dvw - 600px);
    z-index: 2;
}

.navigation-overlay > div {
    box-shadow: rgba(0, 0, 0, 0.2) 0 8px 24px;
}

/**
  * Additional styles for the Site and Block editor
 */
.is-root-container .gb-accordion__item:not(.has-child-selected) > .gb-container:not(.gb-accordion__toggle) {
    display: none;
}

.is-root-container .gb-accordion__item.has-child-selected > .gb-container:not(.gb-accordion__toggle) {
    display: block;
    padding-left: 0;
    padding-right: 0;
}

.editor-styles-wrapper .is-root-container .navigation-overlay {
    top: 50px !important;
}

.editor-styles-wrapper .navigation-overlay > div {
    max-width: none;
    left: 50%;
    top: 50px;
    translate: -50%;
}