CSS Dark Mode Generator
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.
Dark Mode Generator
This color determines the contrast targets for your dark mode variables.
Dark Mode Preview
⚠️ Skipped non-color variables:
How to use:
- Paste your CSS: Copy your
:rootvariables (Hex, RGB, or HSL) into the text area. - Define Background: Select your current light-mode background color to ensure accurate contrast calculations.
- 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.
- 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:
| Method | Browser Support | Best For... |
|---|---|---|
| @media (prefers-color-scheme) | 97%+ (Universal) | Standard projects requiring maximum compatibility. Automatically follows OS settings. |
| .dark-mode Class | 100% (Legacy to Modern) | Projects with a manual toggle switch. Essential for saving user preference via localStorage. |
| light-dark() | ~85% (Modern) | Future-proof projects. Simplifies syntax by keeping light and dark values in a single line. |
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
- Define your Background: For the most accurate inversion, ensure the Background Color input matches your site's actual main body background.
- The "Keep" Strategy: Generally, you should "Keep" status colors (Success Green, Error Red) and only invert structural UI colors (Backgrounds, Borders, Text).
- Global Toggle: If using
light-dark(), remember to addcolor-scheme: light dark;to your:rootselector.
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.
Frequently Asked Questions
What is CSS dark mode and how does it work?
CSS dark mode is a set of styles that replace light backgrounds, dark text, and bright UI colors with darker equivalents - typically dark backgrounds with light text - to reduce eye strain in low-light environments and on OLED screens.
It is implemented in CSS using either the @media (prefers-color-scheme: dark) media query, which automatically applies dark styles when a user's operating system is set to dark mode, or via a manually toggled class (such as .dark-mode) added to the <html> or <body> element using JavaScript.
What is the best way to implement dark mode in CSS?
The most robust approach is to define all your colors as CSS custom properties (variables) on :root, then override them in a dark mode block. This keeps your color logic in one place and avoids hunting through your stylesheet for every hard-coded color value.
For automatic dark mode that follows the operating system setting, wrap your dark variables in @media (prefers-color-scheme: dark). If you want a manual toggle that users can control independently of their OS setting, apply a .dark-mode class to the <html> element via JavaScript and store the preference in localStorage so it persists across page loads.
What is the prefers-color-scheme media query?
prefers-color-scheme is a CSS media feature that detects whether the user has requested a light or dark color scheme at the operating system level. It accepts two values: light and dark. Styles placed inside @media (prefers-color-scheme: dark) are only applied when the user's OS or browser is set to dark mode - no JavaScript is required. It has broad browser support across all modern browsers and is the simplest way to offer automatic dark mode.
What is the CSS light-dark() function?
light-dark() is a modern CSS function that lets you define both a light and a dark color value in a single line, removing the need for a separate @media block. For example, color: light-dark(#000000, #ffffff); applies black in light mode and white in dark mode automatically.
For it to work, you must add color-scheme: light dark; to your :root selector so the browser knows to honour both schemes. Browser support is around 85% as of 2025 - modern browsers support it, but for maximum compatibility a @media fallback is still recommended.
How do I add a dark mode toggle button with JavaScript?
Add a button to your HTML, then use JavaScript to toggle a class on the <html> element and save the user's choice to localStorage so it persists. On every page load, check localStorage first, and fall back to the prefers-color-scheme media query if no saved preference exists. Your CSS then targets the toggled class - for example .dark-mode - to apply the dark variable overrides. To prevent a flash of the wrong theme on load, place the localStorage check in a <script> tag at the very top of your <head>, before any stylesheets are rendered.
Why does my dark mode flash white on page load?
This is known as a Flash of Unstyled Content (FOUC). It happens because the JavaScript that applies your dark mode class runs after the browser has already started rendering the page in light mode. The fix is to move the script that reads localStorage and applies the dark class to the very top of your <head> section, before any CSS link tags. This way the class is applied before the browser paints anything, and no flash occurs.
How do I keep my brand colors the same in dark mode?
Use the "Keep Original" approach - identify which CSS variables represent your core brand colors (primary button color, logo color, accent tones) and exclude them from the dark mode override. Only structural UI colors - backgrounds, borders, text, surface layers - typically need inverting. Status colors like success green and error red are also usually best left unchanged, as users associate those specific colors with meaning and inverting them can cause confusion.
What WCAG contrast ratio is required for dark mode?
The WCAG 2.1 AA standard requires a contrast ratio of at least 4.5:1 between normal text and its background, and at least 3:1 for large text (18pt or 14pt bold). These requirements apply equally in dark mode - a dark background with dark grey text can fail just as easily as a light theme with low contrast. Always check each text/background pairing in your dark palette against these ratios, especially for body text, links, placeholder text, and disabled states.
Should I use CSS variables for dark mode?
Yes - CSS custom properties (variables) are by far the cleanest approach to dark mode. Instead of writing separate selectors for every element in both light and dark contexts, you define your colors once as variables on :root and then simply redefine those same variable names inside your dark mode block. Every element that references a variable automatically updates when the variable changes, keeping your stylesheet maintainable and your dark mode logic in one place.
How do I handle images and icons in dark mode?
For raster images, the CSS filter property can be used selectively - for example, filter: invert(1) hue-rotate(180deg); inverts an image while preserving approximate color fidelity, though results vary by image. A better approach for icons is to use SVG with currentColor so they inherit whatever text color is active. For photographs, it is generally better to leave them as-is rather than inverting them, as inverted photos rarely look natural. If you have separate light and dark versions of a logo or illustration, swap them using the @media (prefers-color-scheme: dark) query or your dark class toggle.
What is the difference between @media prefers-color-scheme and a .dark-mode class?
@media (prefers-color-scheme: dark) automatically follows the user's operating system setting with no JavaScript needed, but gives the user no way to override it on your site specifically.
A .dark-mode class toggled by JavaScript gives users explicit control via a toggle button, independent of their OS setting, and can be saved to localStorage for persistence. The two approaches are not mutually exclusive - a common pattern is to default to the OS preference via the media query but allow users to override it with a manual toggle that sets the class and saves to localStorage.