How can I make corners and squares be borders?

:root {
  --size: 8px;
  --r: -3px;
}

.wrapper {
  position: relative;
  border: 1px solid black;
  margin: 25px auto;
  padding: 2px;
  width: max-content;
}

.inner {
  padding: 15px 25px;
  border: 1px solid black;
}

.conner {
  position: absolute;
  height: var(--size);
  width: var(--size);
  background-color: black;
}

.bottom {
  bottom: var(--r);
}

.right {
  right: var(--r);
}

.top {
  top: var(--r);
}

.left {
  left: var(--r);
}

<div class="wrapper">
  <div class="inner">qwerty</div>
  <div class="conner top left"></div>
  <div class="conner top right"></div>
  <div class="conner bottom left"></div>
  <div class="conner bottom right"></div>
</div>