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HTML 

              
                <div class="confetti"></div>
!

CSS 

              
                .confetti {
  position: relative;
  box-shadow: 0 1px 8px rgba(0,0,0,0.2);
  border-radius: 6px;
  background: #000;
  width: 200px;
  height: 200px;
}

.confetti > span {
  display: block;
  position: absolute;
  opacity: 0;
}

.confetti > span > span {
  display: block;
  width: 100%;
  height: 100%; }

.confetti > span > span > span {
  display: block;
  width: 100%;
  height: 100%;
}

@keyframes rotateY {
  0% {
    transform: rotateY(0deg);
  }
  100% {
    transform: rotateY(360deg);
  }
}

@keyframes rotate360 {
  0% {
    transform: rotate(0deg);
  }
  100% {
    transform: rotate(360deg);
  }
}

/****** Base style. ******/
body {
  display: flex;
  height: 100vh;
  justify-content: center;
  align-items: center;
  margin: 0;
}
!

JS 

              
                class Congratulation {
  constructor($elm) {
    this.$area = $elm;
    this.id = 'congratulation-style';
    this.height;
    this.color = [ // 12カラー
      "#3181A8",
      "#FCEE3D",
      "#D4297E",
      "#D94724",
      "#93CBCE",
      "#3D9148",
      "#E79549",
      "#E397AD",
      "#93CBCE",
      "#D2B155",
      "#AC7DB1",
      "#F5C532"
    ];
    this.OPTION = {
      BREAK_POINT: 768,
      ADD_HEIGHT: 70, // 紙吹雪が降る範囲はエリア高＋この高さ
      SPEED_LEVEL: 25, // 小さくするほど速くなる
      PC_QUANTITY: 100, // BREAK_POINT以上での紙吹雪の総枚数
      SP_QUANTITY: 75 // BREAK_POINT以下での紙吹雪の総枚数
    }
    this.isPC;
  }
  updateDevice() {
    let width = window.innerWidth;
    if (width >= this.OPTION.BREAK_POINT) {
      if (this.isPC) return;
      this.isPC = true;
    } else {
      if (!this.isPC) return;
      this.isPC = false;
    }
  }
  addStyle() {
    // styleタグを作成
    const css = document.createElement('style');
    css.media = 'screen';
    css.type = 'text/css';
    css.id = this.id;
    let rulesStr = '';
    // 移動のkeyframes定義
    for (let i = -6; i < 6; i++) {
      // moving-1 ～ moving-12 を生成
      rulesStr +=
        '@keyframes moving-' + parseInt(i+7, 10) + ' {' +
        '0% { opacity: 0; transform: translate(0, 0); }' +
        '10% { opacity: 1; }' +
        '90% { opacity: 1; }' +
        '100% { opacity: 0; transform: translate(' + i*10 + 'px, ' + (this.height + this.OPTION.ADD_HEIGHT) + 'px); }' +
        '}';
    }
    // ルールをstyleタグに追加
    const rules = document.createTextNode(rulesStr);
    css.appendChild(rules);
    // head内に作成
    document.getElementsByTagName('head')[0].appendChild(css);
  }
  restart() {
    $(this.id).remove(); // <head>の<style>タグを削除
    this.$area.empty(); // 紙吹雪要素を削除
    this.create(); // <style>生成とHTMLタグ生成を再実行
  }
  create() {
    this.height = this.$area.innerHeight();
    // スタイルの生成
    this.addStyle();
    // 上から下まで落ちるミリ秒数（エリア高 * スピードレベル + ランダム<0~9> * 100<ミリ秒化>）
    const duration = this.height * this.OPTION.SPEED_LEVEL + (Math.floor(Math.random() * 10)) * 100;
    // durationを3分割して、アニメーション開始タイミングを3回に分ける
    let index = 0;
    const timer = setInterval(() => {
      let html = '';
      const QUANTITY = this.isPC ? this.OPTION.PC_QUANTITY : this.OPTION.SP_QUANTITY;
      for (let i = 0; i < Math.floor(QUANTITY / 3); i++) {
        // 1階層目のスタイル生成
        const keyframe = 'moving-' + (Math.floor(Math.random() * 12) + 1); // 0の生成を防ぐ
        const delay = duration / (Math.floor(Math.random() * 10));
        const outerStyle = [
          'top: -20px;',
          'left: ' + Math.floor(Math.random()*100) + '%;',
          'width: ' + (Math.floor(Math.random()*4) + 4) + 'px;',
          'height: ' + (Math.floor(Math.random()*4) + 4) + 'px;',
          'animation: ' + keyframe + ' ' + duration + 'ms linear infinite;',
          'animation-delay: ' + delay + 'ms;'
        ];
        // 2階層目・3階層目のスタイル生成
        const color = this.color[Math.floor(Math.random() * 12)];
        const rotateKeyframe = Math.floor(Math.random() * 2) ? 'rotateY' : 'rotate360';
        const innerRotateStyle = rotateKeyframe === 'rotateY' ? 'transform: rotate(' + Math.floor(Math.random() * 60) + 'deg);' : '';
        const bodyStyle = [
          'background-color: ' + color + ';',
          'animation: ' + rotateKeyframe + ' 500ms linear infinite;',
          'animation-delay: ' + delay + 'ms;'
        ];
        // html生成
        html +=
          '<span style="' + outerStyle.join(' ') + '">' +
          '<span style="' + innerRotateStyle + '">' +
          '<span style="' + bodyStyle.join(' ') + '"></span>' +
          '</span>' +
          '</span>';
      }
      this.$area.append(html);

      index += 1;
      if (index >= 2) {
        clearInterval(timer);
      }
    }, duration / 3);
  }
  init() {
    this.isPC = window.innerWidth >= this.OPTION.BREAK_POINT;
    this.create();

    $(window).on('resize', () => {
      const w = window.innerWidth;
      setTimeout(() => {
        if (w === window.innerWidth) {
          this.updateDevice();
          this.restart(); // ウィンドウリサイズ時は紙吹雪を作り直し
        }
      }, 200);
    });
  }
}

/*
 * 紙吹雪を舞わせる.
 */
const $congratulationElm = $('.confetti');
let congratulation = [];
for (var i = 0; i < $congratulationElm.length; i++) {
  congratulation.push(
    new Congratulation($congratulationElm.eq(i))
  );
}

/**
 * 実行
 */
const start = () => {
  for (let i = 0; i < congratulation.length; i++) {
    congratulation[i].init();
  }
};

window.addEventListener('load', () => {
  start();
});
!
999px

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