Christmas Lights Atop the Site

To add some festive things to my sites, I decided to add some Christmas Lights - here is how I did it:

Javascript

// ======================
// CHRISTMAS LIGHTS
// ======================
let christmas = {
    delay: null,
    delete: function(){
        document.body.querySelectorAll('.christmas-lights').forEach(function(ul){
            ul.remove();
        });
    },
    create: function(){
        let h = window.innerWidth / 60 + 2;

        // ✅ Only top
        let data = {
            'top': h
        };

        let ul = null;
        for (let position in data) {
            const count = data[position];
            ul = document.createElement('ul');
            ul.className = 'christmas-lights';
            ul.dataset.position = position;
            for (let i = 0; i <= count; i++) {
                ul.append(document.createElement('li'));
            }
            document.body.append(ul);
        }
    }
};

document.addEventListener('DOMContentLoaded', function(){
    christmas.create();
});

window.addEventListener('resize', function(e) {
    clearTimeout(christmas.delay);
    christmas.delay = setTimeout(function(){
        christmas.delete();
        christmas.create();
    }, 100);
});

CSS

/* CHRISTMAS LIGHTS */
.christmas-lights li {
    --christmas-lights-1: #395c78; /*color - 1*/
    --christmas-lights-2: #bd3b3b; /*color - 2*/
    --christmas-lights-3: #ef9849; /*color - 3*/
    animation-duration: 2s;
    animation-fill-mode: both;
    animation-iteration-count: infinite;
    animation-name: flash-1;
    border-radius: 50%;
    display: inline-block;
    height: 20px;
    margin: 25px 20px;
    position: relative;
    width: 20px;
    will-change: background, box-shadow; 
}
  
.christmas-lights {
    left: 0;
    margin: 0;
    pointer-events: none;
    position: fixed;
    right: 0;
    top: -15px;
    white-space: nowrap;
    width: 100%;
    z-index: 100;
}
  
.christmas-lights[data-position="bottom"] {
    top: auto;
    bottom: -15px;
    transform: scale(-1);
}
  
.christmas-lights[data-position="right"],
.christmas-lights[data-position="left"] {
    transform: rotate(-90deg);
    left: -10px;
    top: 0;
    right: auto;
    bottom: 0;
    width: 100vh;
}
  
.christmas-lights[data-position="right"] {
    transform: rotate(90deg);
    left: auto;
    right: -15px;
}
  
.christmas-lights li:before {
    content: "";
    position: absolute;
    background: #505050;
    width: 10px;
    height: 10px;
    border-top-left-radius: 5px;
    border-top-right-radius: 5px;
    top: -9px;
    left: 5px;
}
  
.christmas-lights li:after {
    content: "";
    top: -23px;
    left: 10px;
    position: absolute;
    width: 60px;
    height: 20px;
    border-bottom: solid #505050 2px;
    border-radius: 50%;
}
  
.christmas-lights li:last-child:after {
    content: none;
}
  
.christmas-lights li:first-child {
    margin-left: -40px;
}

/* OPTIMIZED: Reduced blur from 24px to 12px for performance */
.christmas-lights li:nth-child(2n+1) {
    background: var(--christmas-lights-1);
    box-shadow: 0px 5px 12px 3px rgb(249 212 129); 
    animation-name: flash-2;
    animation-duration: 0.4s;
}
  
.christmas-lights li:nth-child(4n+2) {
    background: var(--christmas-lights-2);
    box-shadow: 0px 5px 12px 3px var(--christmas-lights-2);
    animation-name: flash-3;
    animation-duration: 1.1s;
}
  
.christmas-lights li:nth-child(odd) {
    animation-duration: 1.8s;
}
  
.christmas-lights li:nth-child(3n+1) {
      animation-duration: 1.4s;
}
  
@keyframes flash-1 {
    0%, 100% {
        background: var(--christmas-lights-1);
        box-shadow: 0px 5px 12px 3px var(--christmas-lights-1);
    }
    50% {
        background: var(--christmas-lights-2);
        box-shadow: 0px 5px 12px 3px var(--christmas-lights-2);
    }
}
  
@keyframes flash-2 {
    0%, 100% {
        background: var(--christmas-lights-2);
        box-shadow: 0px 5px 12px 3px var(--christmas-lights-2);
    }
    50% {
        background: var(--christmas-lights-3);
        box-shadow: 0px 5px 12px 3px var(--christmas-lights-3);
    }
}
  
@keyframes flash-3 {
    0%, 100% {
        background: var(--christmas-lights-3);
        box-shadow: 0px 5px 12px 3px var(--christmas-lights-3);
    }
    50% {
        background: var(--christmas-lights-1);
        box-shadow: 0px 5px 12px 3px var(--christmas-lights-1);
    }
}
 
@media (max-width: 1024px){
  .christmas-lights[data-position="left"] {
      left: -14px;
  }
 
  .christmas-lights[data-position="right"] {
      right: -14px;
  }
   
  .christmas-lights[data-position="left"],
  .christmas-lights[data-position="right"] {
    height: 100vh;
  }
}

/* ---- OPTIMIZATION FOR MOBILE ---- */
@media (max-width: 768px) {
  .christmas-lights li {
    /* 1. Kill the glow on mobile to save GPU */
    box-shadow: none !important; 
    
    /* 2. Slow down the blinking. 0.4s is too fast for old CPUs */
    animation-duration: 2s !important; 
  }
}

/* ---- REDUCED MOTION PREFERENCE ---- */
@media (prefers-reduced-motion: reduce) {
  .christmas-lights li {
    animation: none !important;
  }
}