.spoiler, .spoiler a {
  color: black;
  background-color: black;
}

.spoiler:hover, .spoiler:hover a {
  color: gray;
}

/* https://flaviocopes.com/css-system-fonts */
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto",
  "Oxygen", "Ubuntu", "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji",
  "Segoe UI Emoji", "Segoe UI Symbol";
}