There are several userscripts to block those.

<https://github.com/brownie-in-motion/hn-adblock>, discussed: <https://news.ycombinator.com/item?id=31597486>

Another: <https://gist.github.com/pxeger/4aed4baaa87028a2ecc6441a84a1f...>

(I've used neither.)

I've briefly looked into managing these through CSS alone. Not obviously that I can tell, though the text of job listings should match the pattern:

  <company> (YC <class> ) Is Hiring <position>

I think CSS can act based on content, but need to look at selectors for that.

SO suggests not: <https://stackoverflow.com/questions/1520429/is-there-a-css-s...>

HN doesn't assign a distinctive class to these posts, though the "votelinks" class is missing, which can be used to highlight the listings. E.g.:

  /* HN startup job ads */

  .athing td:nth-of-type(2):not(.votelinks) {
      background: #fcc;
  }

  .athing td:nth-of-type(2):not(.votelinks):before {
      content: "Ad";
      position: relative;
      left: 0.4em;
      color: #000;
  } 

(Other properties might be set.)

I'd need to futz with this some more to see if the entire entry could be dropped, though I'd prefer to simply have them stand out, I think...