body {
  font-family: sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;
  margin-top: 50px;
}

.triangle {
  position: relative;
  width: 200px;
  height: 200px;
  margin: 50px 0;
}

.side-a {
  position: absolute;
  bottom: 0;
  left: 0;
}

.side-b {
  position: absolute;
  bottom: 0;
  right: 0;
}

.side-c {
  position: absolute;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
}

input {
  width: 100px;
}