You can use custom css and the core CSS variable to override their styles:
.dd { background-color: var(--bs-gray-700); }
You can find all available CSS variables in the chrome dev tools or from the CSS bundle: https://preview.keenthemes.com/metronic8/demo1/assets/css/style.bundle.css
Also, you can customize custom elements in SASS by adding your custom SCSS file and using global sass variables as explained here.