ダークモードとライトモード

デモ

See the Pen nav 22 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">
            <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 class="nav-toggle" id="navToggle">
                <i id="navIcon" class='bx bx-menu'></i>
            </div>

            <div id="theme" class="theme">
               <i class='bx bxs-sun'></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;
   }

   @media (prefers-color-scheme: dark) {
     body {
          --bg-color: #000;
          --text-color: #fff;
     }
     body.color {
          --bg-color: #fff;
          --text-color: #000;
     }
   }
   @media (prefers-color-scheme: light) {
     body {
          --bg-color: #fff;
          --text-color: #000;
     }
     body.color {
          --bg-color: #000;
          --text-color: #fff;
     }
   }
   
   /* 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;

     fill: var(--text-color);
   }
   
   /* 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: 100;
     display: flex;
     justify-content: center;
     align-items: center;
   }
   
   .nav-toggle {
     font-size: 3rem;
     display: flex;
     align-items: center;
     z-index: 200;
     display: none;
     margin-left: auto;
     padding: .5rem;
   }
   
   .nav-links {
     display: flex;
     align-items: center;
     justify-content: center;
     gap: 2rem;
   }
   
   .nav-links a {
     color: var(--text-color);
   }

   .theme {
     cursor: pointer;
     padding: .5rem;
     color: var(--text-color);
     z-index: 200;
   }
   
   /*スマホサイズナビゲーションバー*/
   @media screen and (max-width: 768px) {
     
     .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'),
    navLink = document.querySelectorAll('.nav-link'),
    theme = document.getElementById('theme')

navToggle?.addEventListener('click', function () {
    if (navIcon.classList.contains('bx-menu')) {
        navIcon.classList.replace('bx-menu', 'bx-x');
        navMenu.classList.toggle('toggle');
    } else {
        navIcon.classList.replace('bx-x', 'bx-menu');
        navMenu.classList.toggle('toggle');
    }
})

navLink.forEach(function (li) {
    li.addEventListener('click', function () {
        navIcon.classList.replace('bx-x', 'bx-menu');
        navMenu.classList.remove('toggle');
    })
})

// theme
if (window.matchMedia('(prefers-color-scheme: dark)').matches === true) {
    theme.firstElementChild.classList = 'bx bxs-sun';
} else {
    theme.firstElementChild.classList = 'bx bxs-moon';
}

theme.addEventListener('click', function () {

    if (window.matchMedia('(prefers-color-scheme: dark)').matches === true) {
        if (document.body.classList.contains('color')) {
            theme.firstElementChild.classList = 'bx bxs-sun';
        } else {
            theme.firstElementChild.classList = 'bx bxs-moon';
        }
    } else {
        if (document.body.classList.contains('color')) {
            theme.firstElementChild.classList = 'bx bxs-moon';
        } else {
            theme.firstElementChild.classList = 'bx bxs-sun';
        }
    }
    document.body.classList.toggle('color');
})