body {
  background-color: black;
  color: white;
  font-family: Verdana;
}

.border-outer {
  background-color: white;
  clip-path: polygon(5% 0%, 95% 0%, 100% 5%, 100% 95%, 95% 100%, 5% 100%, 0% 95%, 0% 5%);
}

.border-inner {
  background-color: black;
  clip-path: polygon(10% 10%, 90% 10%, 90% 90%, 10% 90%);
}

.border-inside {
}