• Completely remove the background image
  

  body.ContentBoxBody { background: url(); }

• Fill the page with your default site background image
  

  body.ContentBoxBody { background-repeat: repeat; }
  body.ContentBoxBody div.ContentBoxBody { background: transparent; }

• Change the background color, no image (adjust color in blue)
  

  body.ContentBoxBody, body.ContentBoxBody div.ContentBoxBody { background: #000000 url(); }

#lbltitle { padding-left: 40px; color: #00b0f0; }
#lblDetails { display: block; padding: 10px 40px; color: #ffffff;}

• Title:
  #lbltitle targets the title of the popup window... adjust the color (in blue) and padding value (in red) as desired - the "padding-left: 40px" matches the second number of the #lblDetails to keep the left side aligned.
• Content:
  #lblDetails targets the info content inside the popup window. The display block is necessary to get the css padding to work properly. Adjust the color (in blue) or adjust the padding (in red) as desired - "10px 40px" is a CSS shortcut which means, set the top and bottom padding to 10px, then set the left and right padding to 40px. The long version would be this: "10px 40px 10px 40px" which gives the dimensions of the top, right, bottom & left sides in that order.

background: #ffffcc url();