.card.inactive {
    position: relative;
    opacity: 0.5; /* faded look */
    filter: grayscale(100%); /* optional: greyed out */
}

    .card.inactive::after {
        content: "";
        position: absolute;
        top: 50%;
        left: 50%;
        transform: translate(-50%, -50%) rotate(-20deg);
        background-image: url('/path/to/watermark.png');
        background-size: contain;
        background-repeat: no-repeat;
        width: 200px;
        height: 200px;
        opacity: 0.15;
        pointer-events: none;
    }