.coin {
    
    width: 32px;
    height: 32px;
    
    position: absolute;
   
    background-image: url('../images/coin.png');
    background-size: cover;
    pointer-events: none;
    transform: translate(-50%, -50%);
    will-change: transform, opacity;

}
/* 高級金屬微光 */
@keyframes coinGlow {
    0%   { filter: brightness(1); }
    50%  { filter: brightness(1.25); }
    100% { filter: brightness(1); }
}

#particle-layer {
     position: fixed;   /* 跟著頁面滾動 */
    top: 0;
    left: 0;
    width: 100%;
   height: auto;        /* ❗固定一個可視高，不要 auto */
    pointer-events: none;
    overflow: visible;
    z-index: 9999;
}