<br> problem

HTML

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/Swiper/4.5.0/css/swiper.min.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/Swiper/4.5.0/js/swiper.min.js"></script>
<!-- The corresponding part is at the bottom. (It is faster to count from the bottom)
(There is a mark in the comment) -->

<div class="solid-ti"></div>

<div id="wrap">
  <div id="left">
    <h1 class="title">動と静を共有する椅子「Rollse」</h1>

    <div class="swiper-pagination"></div>
    <div class="swiper-container swiperCnt max">
      <div class="swiper-wrapper imgs max-inner">
        <div class="swiper-slide"><img class="work" src="http://placehold.jp/45/1920a6/ffffff/693x350.png?text=1" alt="Rollse-logo" /></div>
        <div class="swiper-slide"><img class="work" src="http://placehold.jp/45/199fa6/ffffff/693x350.png?text=2" alt="Rollse-killer" /></div>
        <div class="swiper-slide"><img class="work" src="http://placehold.jp/45/a61972/ffffff/693x350.png?text=3" alt="Rollse-data" /></div>
        <div class="swiper-slide"><img class="work" src="http://placehold.jp/45/a6a619/ffffff/693x350.png?text=4" alt="Rollse-image" /></div>
      </div>
    </div>

    <div class="L-under">
      <div class="mis">
        <h3 class="mission">MISSION:</h3>
        <p class="m-p">触覚に訴えるプロダクト　　　▶︎ 3人チームの1人が、この触り心地を発見</p>
      </div>

      <div class="solid-mc"></div>

      <div class="con">
        <h2 class="concept">CONCEPT:</h2>
        <p class="c-p">緊張感のある空間をつくる。</p>
      </div>

      <div class="what">
        <img src="http://placehold.jp/45/d4d4d4/d4d4d4/28x20.png?text=_" alt="2nd" /><img src="http://placehold.jp/45/d4d4d4/d4d4d4/20x20.png?text=_" alt="ai" /><img src="http://placehold.jp/45/d4d4d4/d4d4d4/20x20.png?text=_" alt="vw" />

        <span>企画</span>
        <span>雑貨の設計</span>
        <span>ネーミング</span>
        <span>文章</span>
        <span>展開</span>
      </div>
    </div>
  </div>

  <div id="right">
    <div class="top">
      <div class="cat">
        <h5...

CSS

/* The corresponding part is at the bottom too. (It is faster to count from the bottom)
(There is a mark in the comment) */


html {
  font-size: 62.5%;
  height: 100%;
}

body {
  font-size: 1.5rem;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  background-color: #c6d2dd;
  color: white;
}

#wrap {
  display: flex;
  width: 100%;
  height: 100vh;
  padding: 1.8rem 4.7rem 2.7rem 2.4rem;
}

h2, h3, h4, h5, h6 {
  display: inline;
}

.mission, .m-p, .concept, .c-p, .what, .target, .t-p, .main-p, .nb, .nb-p, .period, .p-p, .category, .cg-p, .class, .cl-p, .release, .r-p, .nbb, .per, .cat, .cla, .rel {
  display: inline-block;
}

#left, #right {
  display: flex;
  flex-direction: column;
  height: 100%;
  max-height: 100%;
}

#left {
  width: 57%;
}

#right {
  position: relative;
  width: 43%;
  padding-left: 6.5rem;
}

.title {
  height: 3.55rem;
  font-size: 1.8rem;
  padding-bottom: 1.7rem;
}

.solid-ti {
  position: absolute;
  width: 100%;
  border-top: 0.1rem solid white;
  margin-top: 5.35rem;
}

.solid-mc {
  border-bottom: 0.1rem solid white;
  margin-left: -2.4rem;
}

.solid-tm {
  border-bottom: 0.1rem solid white;
  margin-right: -4.7rem;
}

.swiper-pagination {
  top: 6rem;
}

.max {
  position: relative;
  width: 100%;
  flex: 1;
}

.max-inner {
  position: absolute;
  width: 100%;
  height: 100%;
}

.swiper-slide {
  display: flex;
  align-items: center;
}
.swiper-slide img {
  width: 100%;
}

.swiperP {
  height: auto;
}

.swiper-pagination-bullet {
  background: none;
  font-size: 1rem;
  margin-right: 0.5rem;
  opacity: 0.3;
}
.swiper-pagination-bullet::before {
  content: "0";
  font-weight: bold;
}
.swiper-pagination-bullet:hover::before {
  content: "1";
  font-weight: bold;
}

.swiper-pagination-bullet-active {
  background: none;
  transform: scale(1);
  transition-duration: 0.16s;
  opacity: 0.7;
}
.swiper-pagination-bullet-active::before {
  content: "1";
  font-weight: bold;
}

.mis {
  padding: 2.6rem 0...

JavaScript

/* 1 */
// Get the center of the height of .main
const rect = document.getElementsByClassName("main")[0].getBoundingClientRect();
console.log(rect)
const mainHCenter =rect.top +( rect.height / 2);
const mainWCenter =rect.left +( rect.width / 2);

console.log(mainHCenter);  // Match

// Get the element at the center of the height of .main
var centerElm = document.elementFromPoint(mainWCenter, mainHCenter);

console.log(centerElm);  // Wrong


/* 2 */
/*
// Get the center of the height of .main
const main = document.querySelector(".main");
const centerY = main.offsetHeight / 2;
const centerX = main.offsetWidth / 2;

console.log('h:' + centerY + 'w:' + centerX);  // Almost match

// Get the element at the center of the height of .main
const element = document.elementFromPoint(centerX, centerY);

console.log(element);  // Wrong
*/



/* swiper (doesn't matter) */
var swiperCnt = new Swiper('.swiperCnt', {
  direction: 'vertical',
  autoHeight: true,
  pagination: {
    el: '.swiper-pagination',
    type: 'bullets',
    clickable: 'true',
  },
  keyboard: {
    enabled: true,
  },
  mousewheel: {
    forceToAxis: true,
    invert: true,
  },
  renderBullet: function(index, className) {
    return '<span class="' + className + '">' + (index + 1) + '</span>';
  },
});


$(function() {
  var that;
  var i = 0;
  var j = $(".main > p").length - 1;
  $('.mai').bind('mousewheel', function(e) {
    if (e.originalEvent.wheelDelta < 0) {
      //scroll down
      i++;
      if (i >= j) {
        i = j;
      }
      if (i <= j) {
        $(".main > p").each(function(i) {
          if ($(this).hasClass('active')) {
            if ($(this).hasClass(i)) {
              if (i < j) {
                that = $(this).next();
              } else {
                that = $(this);
              }
            }
          }
          $(this).removeClass('active');
        });
        $(that).addClass('active');
      }
    } else {
      //scroll up
      i--;
      if (i <= 0) {
       ...