All phpBB 3.1 styles available on this website use .scss stylesheets instead of usual .css files. After editing any .scss file you need to recompile it. Unfortunately that process requires external tools because there is no decent SASS compilers for PHP. Now this process is easier! I present Sass compiler for phpBB! Sass compiler is an extension for phpBB 3.1. It adds new tab to admin control panel where you can see all styles that use .scss files and link to recompile stylesheet. Screenshot below. You no longer need to install any third party software to recompile stylesheets. I did that for you. I have installed all required software on one of my servers. This phpBB extension connects to my server, asks it to compile .scss files and sends back compiled stylesheet. Download link: click here GitHub repo: click here Extension requirements: Your server must support CURL and JSON extensions. Those extensions are usually supported, but some hosts might disable them for whatever reason. phpBB must have write access to file theme/stylesheet.css in style you are compiling. Internet connection when compiling stylesheet. If it cannot connect to my server, it cannot compile stylesheet. Installation: Unpack zip file Upload contents to directory "ext" on your forum. If you upload it correctly, you should see file ext/arty/scss/composer.json In admin control panel click "customize" tab, install extension.