#masonry {
   width: 100%;
   margin: 0 auto;
}

.grid-sizer, .grid-item {
   width: calc(25% - 4px);
   margin-bottom: 3px;
}

.grid-item img {
   width: 100%;
   display: block;
}

/* Media Query for Mobile Devices */
@media (max-width: 600px) {
   .grid {
     margin-left: 0; /* Reset margin for mobile */
     width: 100%; /* Reset width for mobile */
   }

   .grid-item {
     width: 100%; /* Full width for single column */
     margin-left: 0; /* Reset margin for mobile */
   }
 }

 #myBtn {
   display: none;
   position: fixed;
   bottom: 20px;
   left: 30px;
   z-index: 99;
   font-size: 18px;
   border: none;
   outline: none;
   background-color: red;
   color: white;
   cursor: pointer;
   padding: 15px;
   border-radius: 4px;
 }
 #myBtn:hover {
   background-color: #454545;
 }