Initial setup Make sure the Ghostscript is installed on your system. Make sure the Ghostscript path is correct in your config.php. Make sure the Zlib library is installed on your system. Create a course or use the existing one. Create a student account or use the existing one. Create an Assignment activity, make sure Annotate PDF is checked in the Feedback types section. Testing Log in as a student account. Go to the Assignment activity. Submit a PDF file. Log in as a teacher/admin account. Go to the Assignment activity. Click on the Grade button. Verify that you will see three navigation buttons in the bottom right corner. Verify that the colour contrast of the buttons is now 5.47:1 ( Greater than 3:1 ) Using the DevTools, inspect a light grey background button and copy the value of the background-color property Click the right button on a layout selector icon and open it in a new tab In the new tab, click the right button again on the layout selector icon and choose "Inspect" In the elements panel of the DevTools inspector, confirm you see something like <path xmlns="http://www.w3.org/2000/svg" style="fill:#495057;" ... ** Copy the number after "fill"; that's the icon (foreground) colour Got to https://webaim.org/resources/contrastchecker/ Carry on the test using as foreground color the icon one and as background color the color of the button.