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HTML

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About the <head>

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Insecure Resource

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CSS

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CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

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JavaScript

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JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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HTML 

              
                <button type="button" id="menu-button" aria-expanded="false" aria-controls="menu" aria-label="メニュー">
  <span class="bar"></span>
  <span class="menu-label" id="menu-label" aria-hidden="true">MENU</span>
</button>
<div id="overlay"></div>
<nav id="menu" inert>
  <ul class="test">
    <li><a href="#">メニュー項目1</a></li>
    <li><a href="#">メニュー項目2</a></li>
    <li><a href="#">メニュー項目3</a></li>
    <li><a href="#">メニュー項目4</a></li>
    <li><a href="#">メニュー項目5</a></li>
  </ul>
</nav>
<main>
  <section class="section">section1</section>
  <section class="section">section2</section>
</main>
!

CSS 

              
                /* ハンバーガーメニュー */
#menu-button {
  position: fixed;
  right: 8px;
  display: grid;
  place-items: center;
  place-content: center;
  width: 60px;
  height: 60px;
  background: #ddd;
  border: none;
  cursor: pointer;
  z-index: 999;
}

/* バー */
.bar,
.bar::before,
.bar::after {
  width: 25px;
  height: 3px;
  background-color: #333;
  transition: transform 0.3s;
}

.bar {
  display: grid;

  &::before,
  &::after {
    content: "";
    grid-area: 1 / 1;
  }

  &::before {
    transform: translateY(-8px);
  }

  &::after {
    transform: translateY(8px);
  }
}

/* オープン時のバー */
.menu-open {
  .bar {
    background-color: transparent;

    &::before {
      transform: rotate(45deg);
    }

    &::after {
      transform: rotate(-45deg);
    }
  }
}

/* メニューラベル */
.menu-label {
  transform: translateY(10px);
  font-size: 10px;
  color: #333;
}

/* オーバーレイ */
#overlay {
  visibility: hidden;
  opacity: 0;
  position: fixed;
  inset: 0;
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.5);
  z-index: 997;
  transition: opacity 0.3s;

  /* オープン時のオーバーレイ */
  .menu-open & {
    visibility: visible;
    opacity: 1;
  }
}

/* メニュー */
#menu {
  position: fixed;
  height: 100%;
  width: 300px;
  background-color: #fff;
  right: 0;
  top: 0;
  z-index: 998;
  overflow-y: auto;
  transform: translateX(100%);
  transition: transform 0.3s ease-out;

  & ul {
    list-style: none;
    padding: 0;
    margin: 80px 0 0 0;
  }

  & li {
    padding: 20px;
  }

  & a {
    color: #333;
  }
}

/* オープン時のメニュー */
.menu-open #menu {
  transform: translateX(0);
}

/* body */
body {
  overflow-x: clip;

  /* オープン時のbody */
  .menu-open& {
    overflow: clip;
  }
}

/* コンテンツ */
.section {
  width: 100%;
  height: 70vh;
  background-color: #bbb;
  display: grid;
  place-items: center;
  font-size: 2em;

  &:nth-child(2) {
    background-color: #ccc;
  }
}
!

JS 

              
                const menuButton = document.getElementById("menu-button");
const menuLabel = document.getElementById("menu-label");
const menu = document.getElementById("menu");
const body = document.body;
const overlay = document.getElementById("overlay");

function toggleMenu() {
  if (!body.classList.contains("menu-open")) {
    body.classList.add("menu-open");
    menuButton.setAttribute("aria-expanded", "true");
    menuButton.setAttribute("aria-label", "閉じる");
    menu.inert = false;
    if (menuLabel) {
      menuLabel.textContent = "CLOSE";
    }
  } else {
    body.classList.remove("menu-open");
    menuButton.setAttribute("aria-expanded", "false");
    menuButton.setAttribute("aria-label", "メニュー");
    menu.inert = true;
    if (menuLabel) {
      menuLabel.textContent = "MENU";
    }
  }
}

if (menuButton) {
  menuButton.addEventListener("click", toggleMenu);
}

if (overlay) {
  overlay.addEventListener("click", toggleMenu);
}
!
999px

Console