Hello,

Try this code. Add the code to the Theme Settings > Custom CSS:

.product-element-top.product-image-link .product-label.featured {
    background-color: #e22d2d;
    font-size: 14px;
    color: #fff;
    font-weight: 600;
min-width: 50px;
}

Change the colors and text size as per your needs.

Best Regards