Now that your theme is available in Liferay, it’s time to dress it up for a stylistic appeal. Currently in the Look and Feel settings, your theme’s thumbnail is a broken image. To remedy this, create a 1080 pixels wide by 864 pixels high image to use as your theme’s thumbnail. You may want to take a snapshot of your theme and resize it to these dimension. It is very important to abide by these exact dimensions or your image will not display properly as a thumbnail. Save the image as a .png file named screenshot.png and place it in your theme’s docroot/_diffs/images directory (create this directory if it doesn’t already exist). On redeployment, your screenshot.png file automatically displays as your theme’s thumbnail.
Now go to the Look and Feel settings. Your theme’s thumbnail should appear there, along with the Classic theme’s thumbnail.
Tip: To achieve the 1080x864 resolution in a new browser window, use the button provided in the Resize Browser web content article displayed on the Welcome page.