:root{
  /* square. the system has no corners except the status dot and the switch track */
  --radius-0:0px;
  --radius-1:0px;
  --radius-2:0px;
  --radius-3:0px;
  --radius-4:0px;
  --radius-pill:999px;

  --hairline:1px;
  --rule-weight:1px;
  --rule-heavy:2px;

  --border-subtle:rgba(10,10,10,.1);
  --border-default:rgba(10,10,10,.18);
  --border-strong:#0a0a0a;
  --border-inverse:rgba(255,255,255,.18);
  --border-focus:#4c9aff;

  --border-card:var(--hairline) solid var(--border-subtle);
  --border-control:var(--hairline) solid var(--border-default);
  --rule-double:var(--hairline) solid var(--border-default);
  --focus-ring:0 0 0 3px rgba(76,154,255,.35);
}