Answer

To edit existing CSS Stylesheet code at Summon Administration Console > SETTINGS > Summon 2.0 External Script > CSS Stylesheet, you first need to save or copy the code from the assets.summon.serialssolutions.com URL.

First, copy the assets.summon.serialssolutions.com URL and paste it into a new browser tab. Next, select the CSS code that is displayed and copy it to your clipboard. At this point, you may also want to paste the copied code into a Notepad file and save an offline copy for safekeeping. 

Once the code has been copied, return to the tab with the Summon Administration Console. Click the 'Edit' button next to the URL in the CSS Stylesheet field. You will notice that it shows a blank text editor. Next, paste into the code you copied to your clipboard into the text editor..

You can modify or add to your existing CSS code. When done with your changes, click the 'Save' button next to the CSS Stylesheet field. Wait for the page to save the CSS Stylesheet as a new assets.summon.serialssolutions.com URL. Finally, click the blue "Save Settings" button at the bottom of the page to save your changes.