.snow-container {
    position: fixed;
    pointer-events: none;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 9999;
}

.snowflake {
    position: fixed;
    top: -10px;
    color: #fff;
    font-size: 7px;
    opacity: 0.8;
    user-select: none;
    will-change: transform;
    animation-name: snow-fall, snow-sway;
    animation-timing-function: linear, ease-in-out;
    animation-iteration-count: infinite, infinite;
}

/* Rơi từ trên xuống dưới */
@keyframes snow-fall {
    0%   { transform: translate3d(0, -100vh, 0); }
    100% { transform: translate3d(0, 110vh, 0); }
}

/* Lắc lư trái phải nhẹ */
@keyframes snow-sway {
    0%   { margin-left: 0;   }
    50%  { margin-left: 20px;}
    100% { margin-left: -20px;}
}