Dark / Light Theme Toggle

Переключатель тёмной и светлой темы с плавной анимацией. Автоматически определяет системную тему при первом посещении. Чистый JS без библиотек.

(function(){
    const root = document.createElement('div');
    document.body.appendChild(root);
    const container = root;

    try {
const host = document.createElement('div');
container.appendChild(host);
const shadow = host.attachShadow({ mode: 'open' });

const style = document.createElement('style');
style.textContent = `
  :host { display: block; font-family: monospace; }

  .demo {
    padding: 24px;
    border-radius: 14px;
    transition: background 0.4s, color 0.4s, border-color 0.4s;
  }
  .demo[data-theme="dark"] {
    background: #0d1117;
    color: #e6edf3;
    border: 1px solid #30363d;
  }
  .demo[data-theme="light"] {
    background: #ffffff;
    color: #1f2328;
    border: 1px solid #d0d7de;
  }

  .header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
  }

  .logo { font-size: 15px; font-weight: bold; letter-spacing: 0.05em; transition: color 0.4s; }
  .demo[data-theme="dark"]  .logo { color: #58a6ff; }
  .demo[data-theme="light"] .logo { color: #0969da; }

  .toggle {
    position: relative;
    width: 56px;
    height: 28px;
    border-radius: 50px;
    cursor: pointer;
    border: none;
    transition: background 0.4s;
    flex-shrink: 0;
  }
  .demo[data-theme="dark"]  .toggle { background: #388bfd44; }
  .demo[data-theme="light"] .toggle { background: #f0c000; }

  .thumb {
    position: absolute;
    top: 3px;
    width: 22px;
    height: 22px;
    border-radius: 50%;
    transition: transform 0.4s cubic-bezier(0.23,1,0.32,1), background 0.4s;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 11px;
    font-weight: bold;
  }
  .demo[data-theme="dark"]  .thumb { transform: translateX(3px);  background: #388bfd; color: #fff; }
  .demo[data-theme="light"] .thumb { transform: translateX(31px); background: #fff; color: #c8a000; }

  .cards {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 10px;
    margin-bottom: 16px;
  }

  .card {
    padding: 14px;
    border-radius: 10px;
    transition: background 0.4s, border-color 0.4s;
  }
  .demo[data-theme="dark"]  .card { background: #161b22; border: 1px solid #30363d; }
  .demo[data-theme="light"] .card { background: #f6f8fa; border: 1px solid #d0d7de; }

  .card-title { font-size: 12px; font-weight: bold; margin-bottom: 4px; transition: color 0.4s; }
  .demo[data-theme="dark"]  .card-title { color: #f0f6fc; }
  .demo[data-theme="light"] .card-title { color: #1f2328; }

  .card-sub { font-size: 11px; transition: color 0.4s; }
  .demo[data-theme="dark"]  .card-sub { color: #8b949e; }
  .demo[data-theme="light"] .card-sub { color: #656d76; }

  .badge {
    display: inline-block;
    margin-top: 8px;
    padding: 2px 8px;
    border-radius: 20px;
    font-size: 10px;
    font-weight: bold;
    transition: background 0.4s, color 0.4s;
  }
  .demo[data-theme="dark"]  .badge { background: #388bfd22; color: #58a6ff; }
  .demo[data-theme="light"] .badge { background: #0969da15; color: #0969da; }

  .code {
    padding: 12px;
    border-radius: 8px;
    font-size: 12px;
    line-height: 1.6;
    transition: background 0.4s, color 0.4s, border-color 0.4s;
  }
  .demo[data-theme="dark"]  .code { background: #010409; color: #79c0ff; border: 1px solid #30363d; }
  .demo[data-theme="light"] .code { background: #f6f8fa; color: #0550ae; border: 1px solid #d0d7de; }

  .label {
    text-align: center;
    font-size: 11px;
    margin-top: 14px;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    transition: color 0.4s;
  }
  .demo[data-theme="dark"]  .label { color: #8b949e; }
  .demo[data-theme="light"] .label { color: #656d76; }
`;

const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
let isDark = prefersDark;

const demo = document.createElement('div');
demo.className = 'demo';
demo.setAttribute('data-theme', isDark ? 'dark' : 'light');

const header = document.createElement('div');
header.className = 'header';

const logo = document.createElement('div');
logo.className = 'logo';
logo.textContent = '> SnippetHub_';

const toggle = document.createElement('button');
toggle.className = 'toggle';

const thumb = document.createElement('div');
thumb.className = 'thumb';
thumb.textContent = isDark ? 'D' : 'L';
toggle.appendChild(thumb);

header.appendChild(logo);
header.appendChild(toggle);

const cards = document.createElement('div');
cards.className = 'cards';
cards.innerHTML = `
  <div class="card">
    <div class="card-title">Typewriter Effect</div>
    <div class="card-sub">Эффект печатающей машинки</div>
    <span class="badge">JS</span>
  </div>
  <div class="card">
    <div class="card-title">Card Component</div>
    <div class="card-sub">Универсальная карточка</div>
    <span class="badge">HTML+CSS</span>
  </div>
`;

const code = document.createElement('div');
code.className = 'code';
code.innerHTML = 'const theme = localStorage.getItem(\'theme\');<br>document.body.setAttribute(\'data-theme\', theme);';

const label = document.createElement('div');
label.className = 'label';
label.textContent = isDark ? 'Dark Mode' : 'Light Mode';

demo.appendChild(header);
demo.appendChild(cards);
demo.appendChild(code);
demo.appendChild(label);

shadow.appendChild(style);
shadow.appendChild(demo);

toggle.addEventListener('click', () => {
  isDark = !isDark;
  demo.setAttribute('data-theme', isDark ? 'dark' : 'light');
  thumb.textContent = isDark ? 'D' : 'L';
  label.textContent = isDark ? 'Dark Mode' : 'Light Mode';
});
    } catch(e){
        console.error(e);
    }
})();

👁 8