Step 1:
Create a rectangular node (see templates in the "Shape Nodes" palette section), set its Line Color to "No Color", and resize the node as desired.
Step 2:
Right-click the new node and choose "Add Label". Select the new label. Change its Background Color and Border Color to "Black", its Insets to "1 0 1 0", its Size to "Fit Node Width, its Distance to "0", and its Placement to "Internal: Top".
Step 3:
Repeat step 2, but use Placement to "Internal: Bottom".
To ease the "select the new label" part, assign the label some dummy text when creating the label. Then complete all modifications and as a last step remove the label's text.