This option allows you to chose this style for the Chat window.
When you hover over this style of chat window with your mouse, the background of the window will darken to make it easier to see the chat text.
Note: The "thumb" or slider control for the scroll bar was made transparent. It still exists between the up and down arrows and can be clicked on and moved up and down. Many of the Chat Fonts may appear fuzzy when viewed on a transparent chat window. You may need to change either the style of the font or the color of the chat message to make the text more clear.