This will grey out all of the visual editor buttons and enable hmtl input.
Then simply paste or enter your html code/embed into the text box.
If you would like to see a preview of your bulletin, click the blue code button again. This will switch back to the visual editor.
Then click post bulletin :)
Mac/Apple: Apple + R or command + R
For mobile users, you should see the most current version of the page but if youre willing to clear your mobile cache: