Dark Mode Toggle

I often work on my blog in the evening and the bright glare of the site is becoming a bit much. So I added a dark mode – its the lamp in the top right corner. Go ahead, click it. It was more involved than I had though and I learned some new CSS and javascript.

This is not so much a guide as it is notes from my journey. For guides I suggest looking at Josh W. Comeau’s The Quest for the Perfect Dark Mode or Dark mode toggle by Jouni Kantola.

Changing Background and Text

First, let’s make a button that changes the colors of the background and text. I’ll do this by changing the values of the CSS variables I’m using.

Ok, so this button now changes the background color and the text. It turned out that I had a lot for hardcoded color values spread out across my css and scss files. The most important ones are now covered by CSS variables, but I really should refactor the whole thing at some point.

My strategy here has been to define for the main elements such as background, button, font, etc. I then define a light and dark version for each and set the default to be light. So for the background color it looks like this:

:root {
    --background-color-light: #fdfdfd;
    --background-color-dark: #222;
    --background-color: var(--background-color-light);

This got a good deal of the way to dark mode. You may have noticed that the button above doesn’t change the colors used for the links, heads, and gradients. That’s because setting those are slightly more complicated.

Changing the Gradients

Over the last few months I’ve been adding more and more color variations to the gradients I use on the site. A gradient is randomly selected every time the page loads. This is a problem for our dark mode since the colors don’t neccesarely go well with a dark background.

Below I’ve selected a couple of gradient that I think goes well with the dark theme. Clicking any of the gradients will set it. If you can’t decide you can click the button and your computer will randomly select one of them for you. I’ve included the gradients used for the light mode as well so you can see how they would look in dark mode.

Dark Mode

Light Mode

Perfect! We can now change the colors on the site inlucding the gradients. This is actually the first time I see these gradient next to each other. Previousely I would just reload the page a bunch of times to see how the gradients look. It’s nice to be able to compare them here.

Persisting the setting

We need to have a way of storing the user preferred setting. But how do we do that without having any backend? This blogpost by Jouni Kantola has an answer – we can use localStorage. LocalStorage is a key/value datastore that’s available on a user’s browser. Like cookies, LocalStorage can only store string data for its keys and values. The datastore is only accessible to JavaScript within that domain and has no expiration time. This is pretty neat, it means that if the user comes back their setting will remain the same – unless they clear their browser’s cache.

Avoiding flickering on page load

Ok, so we can store the users preference, but the CSS doesn’t know anything about this. As I showed above I have CSS variables for the different colors, but the default color is set to use the light mode. We use JavaScript to access localStorage and set the apropriate CSS variables.

But if we aren’t careful the page will be rendered before tha JavaScript changes take effet. This leave to a not-so-suptle flickering of the colors.

Here I’m getting into trouble because of how I store my collection of gradients in a JSON file. This needs to be leads before we can select a color. While this is being loaded the rest of the page renders, and for an instant all the text that rely on the CSS variables default to the font color. This means that links and titles flicker from the current color to the font color and then over to the new color.

My solution here is to set the primiary color to be the background color untill the new colors has been loaded and set. This means that the text fades into the background and back out. This isn’t ideal, but the transition looks smoother then when it flickers into white.

Selecting the button and animation

I’ve been wanting to add more playful elements to my blog and the dark mode toggle seems like a good oppotunity to do so. The button that toggle between dark and light mode should be a nice visual element with a cute On Click animation. Janessa Garrow has a nice blogpost on how she did her Dark Mode Toggle. This Code Pen by @jh3y is also very nice. I like the idea of a light bulb, but I won’t go as far as to implement the tuggable string even though it is a fun element.

A simple toggle with an animation will have to do. I used this Code Pen by Jon Kantner to get started. I stripped most of it away and simply kept the spring-like animation.

It isn’t nearly as nice as this day/night toggle by @ste-vg, but it’s better than the buttons above. Right now the button doesn’t really indicate night\day in any way. I think I will come back to this later and play around with it some more.

Ok, so we have control over all the colors and a toggle to turn it on and off. Everything has been put together in at the right of the page.

Closing thoughts

This was a lot more work than I would have thought. My plan was to spend an evening getting it done, but it ended up taking almost a week.

There is still a bit of polishing to do but I’m very happy with the result. It has been surprisingly fun to look at my content in darkmode. I’m already a big fan of D3.js, but it is really amazing how easy it was for me to get everything working with darkmode. It wouldn’t have been feasibily to update all those figures if I had relyed on static files.