In FlexReportDesigner, you can easily set Borders for Fields, Sections, and Sub-sections. 

To set Border around Fields/Section

1. Select the Field around which you want borders to appear.
2. From the Properties window, select ellipsis next to Borders property. The Borders Properties dialog box opens.
   
3. Select the Line Style and Line Width; select Borders to show - All or - any one or the combination of Left, Top, Right, or Bottom borders. Select the color and click OK.
4. Lets insert borders with rounded corners in the Report Header. Select the Report Header.
5. Set the Line Style, Line Width, Borders, and color as before.
6. Set the Radius X and Radius Y for the corners.
7. Preview the report.
   
   

For inserting rounded corners note that:

• Range of Radius X is from 0 to field's width.
• Range of Radius Y is from 0 to field's height.