JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrap">
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
</div>

CSS

@import url('https://fonts.googleapis.com/css2?family=Neucha&display=swap');


* {
  box-sizing: inherit;
}

html {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: 'Neucha', cursive;
}
.wrap {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(80px, 80px));
  grid-auto-flow: row;
  column-gap: 10px;
  row-gap: 10px;
  width: fit-content;
  max-width: 100%;
  margin-left: auto;
  margin-right: auto;
  background: #999;
}
.item {
  display: inline-block;
  width: 80px;
  height: 80px;
  background: var(--bg-color);
}

JavaScript

const colorBlocks = (block) => {
  const items = document.querySelectorAll(block);
  items.forEach(item => {
    let color = (Math.random().toString(16) + '000000').substring(2, 8).toUpperCase();
    item.style.setProperty('--bg-color', '#' + color);
  })
}

colorBlocks('.item');