body {
    font-family: Arial, sans-serif;
  }

  .grid {
    display: grid;
    width:800px;
    height: 800px;
    grid-template-columns: repeat(auto-fit, minmax(88px, 1fr));
    gap:8px;
    background-color: black;
    border: 5px black solid;
  }


  .grid-item {
    margin:0;
    background-color: white;
    width: 88px;
    height: 88px;
  }
  .grid-item:hover{
    cursor: pointer;
  }
  #AdvertVerti{
    right:20px;
    bottom:20px;
    position:fixed;
    height: 80vh;
    width:auto;   
  }
  #StopButton{
    background-color: rgb(178, 178, 178);
  }
/*While not perfectly made specifically for mobile (What you listed as 640), this was set to what I considered a reasonable number for said change.*/
  @media screen and (max-width: 1000px) {
    #AdvertVerti {
      width:15vw;
      height:auto;
      right:20px;
      bottom: 10px;
      top:auto;
    }
  }