I think I figured out how to do tv-tropes style spoilers in html. now I won't run into trouble when I reveal kills in the last act.
eggbug
bugegg
<details style="position:relative;display: inline-block;border:1px dashed grey;color:white;cursor:pointer;">
<summary style="display:inline;list-style:none;position:relative;z-index:1">
eggbug
</summary>
<div style="background:black;position:absolute;inset:0;z-index:0;"></div></details>