What could be the reason for the appearance of lines on gallery?

On the website made a gallery, here on this example:
https://codepen.io/kitcarver/pen/ZEYdOEZ
everything works fine, but there is a strange line
5e4a89b65e264629289357.png
how can get rid of it?
April 7th 20 at 15:29
0 answer

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