Effortlessly transform your existing light-theme CSS variables into a clean, high-contrast, and accessible dark mode with the CSS Dark Mode Generator. Simply paste in your current :root variables and background color, and the tool intelligently generates a dark-theme equivalent in real time—no manual trial and error required.

Behind the scenes, the generator uses smart HSL-based color inversion logic, preserving each color’s original hue while carefully adjusting lightness and saturation. This approach ensures your brand colors remain instantly recognizable, while still delivering the improved contrast and reduced eye strain users expect from a well-designed dark interface.

Each variable is previewed side-by-side in both light and dark contexts, giving you full visual control over the conversion. You can lock specific colors, fine-tune individual values, or override the generated output entirely—making it easy to strike the perfect balance between brand consistency, readability, and accessibility across all screen types.

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How to use:

1. Paste your CSS: Copy your :root variables (Hex, RGB, or HSL) into the text area.
2. Define Background: Select your current light-mode background color to ensure accurate contrast calculations.
3. Generate & Refine: Review the auto-generated dark variables. Use the "Keep Original" toggle to preserve specific brand colors or use the Color Picker to manually fine-tune individual shades.
4. Export: Choose between standard Media Queries or the modern CSS light-dark() function for your final stylesheet.

Core Features:

• Smart Variable Resolution: Automatically resolves nested var(--reference) dependencies.
• Accessibility First: Real-time WCAG 2.1 Contrast Badges ensure your dark mode stays readable (4.5:1 ratio).
• State Memory: The tool remembers your manual color tweaks even if you toggle back and forth between "Keep" and "Custom."
• Format Aware: Exports variables in the same format (Hex, RGB, HSL) they were imported in.

Technical Details

The Inversion Engine

Unlike a simple "negative" filter that can make colors look muddy or neon, this tool uses Perceptual HSL (Hue, Saturation, Lightness) Transformation.

• Hue Preservation: Your brand's base color remains identical.
• Dynamic Lightness: We flip the lightness scale using a non-linear offset to ensure that very dark colors don't become blindingly bright, and vice-versa.
• Saturation Calibration: Saturation is slightly desaturated in dark mode to prevent "color bleed" on OLED and high-brightness displays.

Reference Resolution (Two-Pass Parsing)

The generator uses a recursive resolver to handle variable aliasing. If you have: --primary: var(--blue); --blue: #3498db; The tool performs a Pass-1 Map to index all values, followed by a Pass-2 Resolve to ensure that --primary is inverted based on the actual hex value of --blue. This prevents broken references in your exported code.

Export Methods

You can choose between two modern implementation strategies:

Accessibility Standards

The tool measures contrast using the WCAG 2.1 algorithm.

• PASS (4.5:1): Meets the AA standard for normal text.
• FAIL (< 4.5:1): Indicated when a color is too dark against the background. We recommend using the manual color picker to lighten these variables until a "PASS" is achieved.

Implementation Tips

1. Define your Background: For the most accurate inversion, ensure the Background Color input matches your site's actual main body background.
2. The "Keep" Strategy: Generally, you should "Keep" status colors (Success Green, Error Red) and only invert structural UI colors (Backgrounds, Borders, Text).
3. Global Toggle: If using light-dark(), remember to add color-scheme: light dark; to your :root selector.

Implementing the Dark Mode Toggle

To use the code generated by this tool, you need a small script to toggle a class on your <html> or <body> tag and save that choice to localStorage.

1. The HTML Toggle

Place this anywhere in your navigation or settings menu.

<button id="theme-toggle" aria-label="Toggle Dark Mode">
  <span class="sun-icon">☀️</span>
  <span class="moon-icon">🌙</span>
</button>

2. The JavaScript (The "Smart" Part)

This script does three things: it checks for a saved preference, checks the system (OS) preference if no save exists, and handles the toggle.

// 1. Identify the toggle button and the root element
const btn = document.getElementById("theme-toggle");
const root = document.documentElement; // This targets the <html> tag

// 2. On load, check localStorage or system settings
const currentTheme = localStorage.getItem("theme");

if (currentTheme === "dark") {
    root.classList.add("dark-mode");
} else if (currentTheme === "light") {
    root.classList.remove("dark-mode");
} else if (window.matchMedia("(prefers-color-scheme: dark)").matches) {
    // If no save, follow the user's OS theme
    root.classList.add("dark-mode");
}

// 3. Handle the click event
btn.addEventListener("click", () => {
    root.classList.toggle("dark-mode");
    
    // Save the choice
    let theme = "light";
    if (root.classList.contains("dark-mode")) {
        theme = "dark";
    }
    localStorage.setItem("theme", theme);
});

3. The CSS Setup

When you export the CSS from this tool, make sure your dark variables are wrapped in the .dark-mode class selector or @media (prefers-color-scheme: dark):

/* Light Mode (Default) */
:root {
  --bg: #ffffff;
  --text: #000000;
}

/* Dark Mode (Applied by JavaScript) */
.dark-mode {
  --bg: #121212;
  --text: #ffffff;
}

body {
  background-color: var(--bg);
  color: var(--text);
  transition: background-color 0.3s, color 0.3s; /* Smooth transition */
}

Why use localStorage?

• Persistence: Without it, every time a user clicks a new link on your site, the theme would reset to light mode (the "Flash of Unstyled Content").
• User Intent: If a user manually toggles your switch, they usually want that choice to override their system settings.

Pro-Tip: Preventing the "Flash"

To prevent a white flash on page load for dark mode users, place the "Check localStorage" part of the script at the very top of your <head> tag, before any CSS or body content is rendered.