MK117 / General LED question

Hi, it’s a while ago since I last used a soldering iron, so forgive me the stupid question.
Before I start assembling the kit, please can someone clarify the LED positioning for me? I clearly see on the print board that the LEDs should have a flat side. This is also shown on the instruction sheet. However, those LEDs that I have carefully examined, are perfectly round - the flat side is missing. So it becomes tricky. I notice that one leg is a bit longer than the other, which I believe is the ‘+’ side, so the shorter leg would be ‘-’. However I am not toally clear in which way the LEDs need to be mounted - becaus there is no flat side.
If someone could please clarify this for me? Thank you!

If you look at the board you see where the print for the LEDs has a flat side.

The shorter leg should go through that side

Brief and clear explanation - thank you! I’ll do it this way.
Best regards!

No problem at all.
Keep an eye on the polarity