You could also find it by looking at the source code to my profile (right click, View Source, ctrl+F, "custom_css")! But here you go:

html, html.legacy, html.legacy *, html:not(.legacy), html:not(.legacy) *, button, input {
  --radius: 0;
}


* {
  font-family: "Noto Mono", monospace;
  font-size: 11pt;
}

.notification {
  background: inherit;
  color: inherit;
  font-size: inherit;
}

button.primary, a.button.primary {
  background: var(--color-lowered);
  color: var(--color-primary);
}

button.primary:hover, a.button.primary:hover, button:not(nav *):hover, a.button:not(nav *):hover {
  background: var(--color-super-lowered)
}

nav, nav:not(.legacy *), nav button, nav a.button, .pillmenu a, .sidenav a {
  padding: 0 0.75rem;
  border: none;
  height: unset;
}

nav button::before, nav a::before, .card:not(:has(form)) button, .card:not(:has(form)) a.button, .card:not(:has(form)) button:not(dialog *), .card:not(:has(form)) a.button:not(dialog *), .avatar {
  border-radius: 0;
}

.pillmenu {
  border: none;
  --radius: 0;
}

.card, .card-nest, .card-nest .card:last-child {
  border: none;
}

::selection {
  background-color: #fff;
  color: hsl(0, 0%, 21%);
}

.response:has(.card:first-of-type[style="display: none"]) .card:last-of-type {
    flex-direction: column-reverse;
}

dialog::backdrop {
  backdrop-filter: brightness(0.4);
  -webkit-backdrop-filter: brightness(0.4);
}

nav:not(.legacy *) a.active::after, nav:not(.legacy *) a:hover::after, .pillmenu:not(.legacy *) a.active::after {
  display: none;
}

nav:not(.legacy *) a.active, nav:not(.legacy *) a:hover {
  color: var(--color-primary-raised)
}

@media screen and (max-width: 900px) {
  .pillmenu:not(.legacy *) {
    top: 48px;
  }
}