body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
  background-color: #f0f0f0;
}

.circulo {
  width: 150px;
  height: 150px;
  border: 2px solid #3498db;
  border-radius: 50%;
  position: relative;
}

.marca {
  width: 10px;
  height: 10px;
  background-color: red;
  border-radius: 50%;
  position: absolute;
}

.marca1 {
  top: 0;
  left: 50%;
  transform: translateX(-50%);
}

.marca2 {
  bottom: 0;
  left: 50%;
  transform: translateX(-50%);
}