背景にオーバーレイ

画面サイズが狭い場合、メニューボタンを押すと、ナビの背後に黒のオーバーレイを出現させます。

デモ

See the Pen nav 4 by logsuke (@design-list) on CodePen.

コード

<!-- Boxicons headタグ内へ -->
<link href='https://unpkg.com/boxicons@2.1.2/css/boxicons.min.css' rel='stylesheet'>

<header class="header" id="header">
        <nav class="nav container">
            <a href="#" class="logo">
                <svg viewBox="0 0 496 512" width="100" title="meh-rolling-eyes">
                    <path
                        d="M248 8C111 8 0 119 0 256s111 248 248 248 248-111 248-248S385 8 248 8zM88 224c0-24.3 13.7-45.2 33.6-56-.7 2.6-1.6 5.2-1.6 8 0 17.7 14.3 32 32 32s32-14.3 32-32c0-2.8-.9-5.4-1.6-8 19.9 10.8 33.6 31.7 33.6 56 0 35.3-28.7 64-64 64s-64-28.7-64-64zm224 176H184c-21.2 0-21.2-32 0-32h128c21.2 0 21.2 32 0 32zm32-112c-35.3 0-64-28.7-64-64 0-24.3 13.7-45.2 33.6-56-.7 2.6-1.6 5.2-1.6 8 0 17.7 14.3 32 32 32s32-14.3 32-32c0-2.8-.9-5.4-1.6-8 19.9 10.8 33.6 31.7 33.6 56 0 35.3-28.7 64-64 64z" />
                </svg>
                logo
            </a>
            <div class="nav-menu" id="navMenu">
                <ul class="nav-links">
                    <li><a href="#section1" class="nav-link">Section1</a></li>
                    <li><a href="#section2" class="nav-link">Section2</a></li>
                    <li><a href="#section3" class="nav-link">Section3</a></li>
                    <li><a href="#section4" class="nav-link">Section4</a></li>
                </ul>

            </div>
            <div id="overlay"></div>

            <div class="nav-toggle" id="navToggle">
                <i id="navIcon" class='bx bx-menu'></i>
            </div>
        </nav>
    </header>

/*=== Base ===*/

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box
}

:root {
  --nav-height: 8rem;
  --max-width: 1024px;
  --container-padding: 0 4rem;
  --gap: 2rem;
  --bg-color: rgb(240, 240, 240);
}

/*=== Font ratio ===*/

html {
  scroll-behavior: smooth;
  font-size: 62.5%;
}

body {
  font-size: 1.6rem;
}

ul {
  list-style: none;
}

a {
  text-decoration: none;
}

/* header */
header {
  width: 100%;
  position: fixed;
  top: 0;
  left: 0;
  z-index: 100;
  background-color: var(--bg-color);
}

.nav svg {
  width: 25px;
  padding: 2px;
  margin-right: 5px;
}

/* nav */
.nav {
  width: 100%;
  max-width: var(--max-width);
  height: var(--nav-height);
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin: 0 auto;
  padding: 0 3rem;
}

.logo,
.nav-toggle {
  color: var(--text-color);
  cursor: pointer;
}

.logo {
  font-weight: bold;
  font-size: 2rem;
  z-index: 200;
  display: flex;
  justify-content: center;
  align-items: center;
}

.nav-toggle {
  font-size: 3rem;
  display: flex;
  align-items: center;
  z-index: 200;
  display: none;
}

.nav-links {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 2rem;
}

.nav-links a {
  color: var(--text-color);
}

#overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(40, 30, 74, 0.459);
  z-index: 110;
  display: none;
}

/*スマホサイズナビゲーションバー*/
@media screen and (max-width: 1024px) {
  
  .nav-menu {
    position: fixed;
    top: 0;
    right: -50%;
    background: var(--bg-color);
    box-shadow: var(--shadow);
    width: 50%;
    height: 100vh;
    padding-top: var(--nav-height);
    transition: transform .5s ease-in-out;
    z-index: 120;
  }

  .nav-menu.toggle {
    transform: translateX(-100%);
  }

  .nav-toggle {
    display: block;
  }

  .nav-links {
    flex-direction: column;
  }

  .nav-links li {
    height: var(--nav-height);
    width: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
  }
}

const navMenu = document.getElementById('navMenu'),
    navToggle = document.getElementById('navToggle'),
    navIcon = document.getElementById('navIcon'),
    overlay = document.getElementById('overlay');

navToggle?.addEventListener('click', function () {
    if (navIcon.classList.contains('bx-menu')) {
        navIcon.classList.replace('bx-menu', 'bx-x');
        navMenu.classList.toggle('toggle');
        overlay.style.display = 'block';
    } else {
        navIcon.classList.replace('bx-x', 'bx-menu');
        navMenu.classList.toggle('toggle');
        overlay.style.display = 'none';
    }
})

const navLink = document.querySelectorAll('.nav-link')

navLink.forEach(function (li) {
    li.addEventListener('click', function () {
        navIcon.classList.replace('bx-x', 'bx-menu');
        navMenu.classList.remove('toggle');
        overlay.style.display = 'none';
    })
})

overlay?.addEventListener('click', function () {
    navIcon.classList.replace('bx-x', 'bx-menu');
    navMenu.classList.remove('toggle');
    overlay.style.display = 'none';
})