<button class="btn-cass">
  <span class="btn-cass-corner" aria-hidden="true"></span>
  <span class="btn-cass-text">SIDE A</span>
</button>

.btn-cass {
  position: relative;
  padding: 14px 32px 14px 38px;
  border: 2px solid #0a0a14;
  border-radius: 0;
  background:
    repeating-linear-gradient(0deg,
      transparent 0 13px,
      rgba(10,10,20,0.18) 13px 14px),
    #ff3d83;
  color: #0a0a14;
  font-family: ui-monospace, monospace;
  font-size: 14px; font-weight: 900;
  letter-spacing: 0.28em;
  cursor: pointer;
  box-shadow: 4px 4px 0 #0a0a14;
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}
.btn-cass-corner {
  position: absolute;
  top: 4px; left: 4px;
  width: 16px; height: 16px;
  background: #00d4d4;
  border: 2px solid #0a0a14;
  transform: rotate(45deg);
  transform-origin: center;
}
.btn-cass-text { position: relative; }
.btn-cass:hover { transform: rotate(-1.5deg) translate(-1px,-1px); box-shadow: 5px 5px 0 #0a0a14; }