Re-enable the Grid and the Snap to Grid. For the following step you will need a grid every 2.5 px. Go to Edit > Preferences > Guides & Grid, and enter 2.5 in the Gridline every box. Now, focus on the top area of your calendar. Pick the Rectangle Tool (M), create a 250 by 60px shape, and place it as shown in the first image.
Fill it with none, but add two similar strokes. A 2pt, white stroke and a 1pt stroke with the color set at R=191 G=185 B=162. Make sure that both strokes are aligned to inside, then go to Effect > Stylize > Rounded Corners. Enter a 10px radius, click OK, then make a copy in front of this shape. Select this copy, remove the two stroke and fill it with the linear gradient shown in the second image.