A darker, more contrasty, Slack theme.
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widget- Merge pull request #35 from Haaroon/master
Fix instructions for slack version 3.0.0+
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custom.css Fix user popups & add backdrop Oct 25, 2017
readme.md fix instructions for slack version 3.0.0+ Dec 18, 2017


Slack Black Theme

A darker, more contrasty, Slack theme.



Installing into Slack

Find your Slack's application directory.

  • Windows: %homepath%\AppData\Local\slack\
  • Mac: /Applications/Slack.app/Contents/
  • Linux: /usr/lib/slack/ (Debian-based)

Open up the most recent version (e.g. app-2.5.1) then open resources\app.asar.unpacked\src\static\index.js

For versions after and including 3.0.0 the same code must be added to the following file resources\app.asar.unpacked\src\static\ssb-interop.js

At the very bottom, add

// First make sure the wrapper app is loaded
document.addEventListener("DOMContentLoaded", function() {

   // Then get its webviews
   let webviews = document.querySelectorAll(".TeamView webview");

   // Fetch our CSS in parallel ahead of time
   const cssPath = 'https://cdn.rawgit.com/widget-/slack-black-theme/master/custom.css';
   let cssPromise = fetch(cssPath).then(response => response.text());

   let customCustomCSS = `
   :root {
      /* Modify these to change your theme colors: */
      --primary: #09F;
      --text: #CCC;
      --background: #080808;
      --background-elevated: #222;

   // Insert a style tag into the wrapper view
   cssPromise.then(css => {
      let s = document.createElement('style');
      s.type = 'text/css';
      s.innerHTML = css + customCustomCSS;

   // Wait for each webview to load
   webviews.forEach(webview => {
      webview.addEventListener('ipc-message', message => {
         if (message.channel == 'didFinishLoading')
            // Finally add the CSS into the webview
            cssPromise.then(css => {
               let script = `
                     let s = document.createElement('style');
                     s.type = 'text/css';
                     s.id = 'slack-custom-css';
                     s.innerHTML = \`${css + customCustomCSS}\`;

Notice that you can edit any of the theme colors using the custom CSS (for the already-custom theme.) Also, you can put any CSS URL you want here, so you don't necessarily need to create an entire fork to change some small styles.

That's it! Restart Slack and see how well it works.

NB: You'll have to do this every time Slack updates.

Color Schemes

Here's some example color variations you might like.



--primary: #09F;
--text: #CCC;
--background: #080808;
--background-elevated: #222;

One Dark

One Dark

--primary: #61AFEF;
--text: #ABB2BF;
--background: #282C34;
--background-elevated: #3B4048;

Low Contrast

Low Contrast

--primary: #CCC;
--text: #999;
--background: #222;
--background-elevated: #444;



--primary: #FFF;
--text: #CCC;
--background: #225;
--background-elevated: #114;

Hot Dog Stand

Hot Dog Stand

--primary: #000;
--text: #FFF;
--background: #F00;
--background-elevated: #FF0;


git clone the project and cd into it.

Change the CSS URL to const cssPath = 'http://localhost:8080/custom.css';

Run a static webserver of some sort on port 8080:

npm install -g static
static .

In addition to running the required modifications, you will likely want to add auto-reloading:

const cssPath = 'http://localhost:8080/custom.css';
const localCssPath = '/Users/bryankeller/Code/slack-black-theme/custom.css';

window.reloadCss = function() {
   const webviews = document.querySelectorAll(".TeamView webview");
   fetch(cssPath + '?zz=' + Date.now(), {cache: "no-store"}) // qs hack to prevent cache
      .then(response => response.text())
      .then(css => {
         webviews.forEach(webview =>
               (function() {
                  let styleElement = document.querySelector('style#slack-custom-css');
                  styleElement.innerHTML = \`${css}\`;

fs.watchFile(localCssPath, reloadCss);

Instead of launching Slack normally, you'll need to enable developer mode to be able to inspect things.

  • Mac: export SLACK_DEVELOPER_MENU=true; open -a /Applications/Slack.app

  • Linux: (todo)

  • Windows: (todo)


Apache 2.0