.background {
      display: flex;
      flex-direction: column;
      height: 100%;
      width: 100%;
      position: absolute;
      top: 0;
      left: 0;
    }

    .row {
      display: flex;
      flex-wrap: nowrap;
      overflow: hidden;
      width: max-content; /* auto expands to fit */
    }

    .row img {
      width: 400px;   /* bigger covers */
      height: 300px;
      object-fit: cover;
      margin: 2px;
    }

    .row .set {
      display: flex;
    }

    /* Speeds: each row uses same keyframe but different durations */
    .row-1 { animation: scroll 40s linear infinite; }
    .row-2 { animation: scroll 60s linear infinite; }
    .row-3 { animation: scroll 80s linear infinite; }
    .row-4 { animation: scroll 100s linear infinite; }

    @keyframes scroll {
      0%   { transform: translateX(0); }
      100% { transform: translateX(-50%); }
    }