SVG: Why cannot show the bars?

Dear all, here I want to draw a series strips ( slim bars), but as can be seen in Dots, the strips cannot be shown. However, if I change to ‘circle’, it works. Could you please tell me where should I modify? Thank you very much in advance!

Thank you evryone. I’ve found the problem. The issue is I didn’t add the ‘height’ property of the strips.