Light/Dark Themes with Manual Switching

Mix.install([
  {:phoenix_playground, "~> 0.1"},
  {:phoenix_html, "~> 4.3"},
  {:autumn, ">= 0.6.0"}
])

HtmlMultiThemes Formatter

Use JavaScript to switch between Light and Dark colors.

defmodule SyntaxHighlighterLive do
  use Phoenix.LiveView

  def mount(_params, _session, socket) do
    code = ~S"""
    @doc "Defines a public function with the given name and body."
    defmacro def(call, expr \\ nil) do
      assert_no_match_or_guard_scope(__CALLER__.context, "def/2")
      define(:def, call, expr, __CALLER__)
    end
    """

    code =
      Autumn.highlight!(
        code,
        language: "elixir",
        formatter:
          {
            :html_multi_themes,
            themes: [light: "github_light", dark: "github_dark"],
            default_theme: "light"
          }
      )

    {:ok, assign(socket, code: code)}
  end

  def render(assigns) do
    ~H"""
    

    
      body {
        min-height: 100vh;
        font-family: ui-monospace,SFMono-Regular,"SF Mono",Menlo,Consolas,"Liberation Mono",monospace;
        transition: background-color 0.3s, color 0.3s;
      }

      html.dark body {
        background: #0d1117;
        color: #e6edf3;
      }

      .theme-buttons {
        margin-bottom: 20px;
        display: flex;
        gap: 10px;
      }

      .theme-button {
        padding: 8px 16px;
        border: 2px solid #ccc;
        background: white;
        color: black;
        border-radius: 6px;
        cursor: pointer;
        font-size: 14px;
      }

      .theme-button:hover {
        background: #f5f5f5;
      }

      html.dark .theme-button {
        background: #21262d;
        color: #e6edf3;
        border-color: #444;
      }

      html.dark .theme-button:hover {
        background: #30363d;
      }

      .theme-button.active {
        background: #0969da;
        color: white;
        border-color: #0969da;
      }

      html.dark .theme-button.active {
        background: #58a6ff;
        color: #0d1117;
        border-color: #58a6ff;
      }

      html.dark .athl,
      html.dark .athl span {
        color: var(--athl-dark) !important;
        background-color: var(--athl-dark-bg) !important;
        font-style: var(--athl-dark-font-style) !important;
        font-weight: var(--athl-dark-font-weight) !important;
        text-decoration: var(--athl-dark-text-decoration) !important;
      }
    

    
      
Manual Light/Dark Theme Switching

      
        
          Light
        
        
          Dark
        
      

      
Click the buttons above to manually switch between light and dark themes.
      
This example uses CSS variables with class-based theme switching.

      {Phoenix.HTML.raw(@code)}
    

    
      function setTheme(theme) {
        const html = document.documentElement;
        const lightBtn = document.getElementById('btn-light');
        const darkBtn = document.getElementById('btn-dark');

        if (theme === 'light') {
          html.classList.remove('dark');
          lightBtn.classList.add('active');
          darkBtn.classList.remove('active');
        } else {
          html.classList.add('dark');
          darkBtn.classList.add('active');
          lightBtn.classList.remove('active');
        }
      }
    
    """
  end
end

PhoenixPlayground.start(live: SyntaxHighlighterLive, open_browser: true, port: 4000)