These "dots appearing only while (not) focused" are known as "extinction illusions", namely
"25 - Appearing Dots"
"26 - Disappearing Dots"
[1] https://www.psy.ritsumei.ac.jp/akitaoka/kieru3e.html#:~:text...
[2] https://www.psy.ritsumei.ac.jp/akitaoka/kieru3e.html#:~:text...
[3] https://codepen.io/myf/full/XjdmJy ( scintillation warning)
[4] https://codepen.io/myf/full/jMqoMW ( scintillation warning)
This is cool, but more as a demonstration of interesting CSS techniques than optical illusions in my opinion.
Also, interestingly, I seem to be able to force myself to "see through" all of these illusions except for induced gradients, which I can't stop seeing unless I cover part of the screen.
33 - color fan: There is another interesting optical illusion here: The fan seems to rotate faster when not directly looking at it.
These are all super dark, for some reason.
You have to actually run them. Otherwise, they're just a dark CodePen preview.
Why the extra step of having to click each one? Only a few of them are interactive.
Because codepens can run javascript. And if a page has 50 of them, it might make the page load time much longer. I know that all these examples are pure CSS, and maybe there is a setting in codepen to disable the "Run" button and automatically run it. Still, getting to decide is generally a better pattern than presuming that that's what the user wants, especially when the fact that the code is inside a codepen makes it explicitly not an integral function of the page. "I thought this was just a blog, and now you want me to run all this javascript??" -- some JS hater, probably.
I appreciate getting to choose as much as possible when code runs.
Somewhat ironically, Codepen ended up introducing the JS execution requirement to view the content.
Wow, this is great!
I want to put some of them in my UIs.
I've often run into these unintentionally messing up my UIs!