No, the subreddit has applied custom css to do that. It's the mildly infuriating subreddit. There's also an image of a hair visible on widescreen monitors, to make you think there's a hair on your display.

I see the hair on my iPhone. That’s a nice touch.

The next step will be adding a web in a corner, to make us think we cracked our touchscreen /s

try eddrit.com

I went there and saw two hairs, and yeah thought it was a nice funny touch.

I then went back to HN and turns out one of the hairs was real and I needed to clean my laptop screen :)

They have a bag of dirty tricks [0], here are a few highlights including a couple already mentioned:

    /* Dead subpixel (Thanks M) */
    .content[role=main]:before {
        content: "";
        position: fixed;
        top: 126px;
        left: 242px;
        width: 1px;
        height: 1px;
        background: #f0f;
        z-index: 9999;
    }

    /* Hair */
    .content[role=main]:after {
        content: "";
        position: fixed;
        top: 150px;
        right: 150px;
        width: 140px;
        height: 200px;
        border-radius: 50%;
        box-shadow: 2px 0 rgb(60, 24, 24, 0.3);
        transform: skewX(-30deg) scale(0.6);
        pointer-events: none;
        z-index: 9999;
    }

    .thing.comment[id*=c] {
        transform: rotate(1deg);
        margin-top: 30px !important;
    }

    .comment p a{
        font-family:Comic Sans MS, Impact,serif;
    }

[0] https://www.reddit.com/r/mildlyinfuriating/wiki/config/style...

r/mildlyinfuriating seems to have a custom stylesheet that is deliberately mildly infuriating.

I see it too. What the heck?