Как можно сделать position: fixed относительно родительского элемента, но не самой страницы?

* {
  font-family: monospace, 'sans-serif';
  padding: 0;
  margin: 0;
}

header {
  height: 100vh;
  background-color: black;
  color: white;
}

.logo {
  margin: auto;
  width: 50vh;
  height: 50vh;
  margin: auto;
  position: relative;
  top: 25vh;
}

.span__logo {
  text-transform: uppercase;
  color: white;
  display: block;
  text-align: center;
  position: relative;
  top: 45%;
  font-size: 40px;
}

.circle__logo {
  border: 2px solid white;
  border-radius: 50%;
  width: 50vh;
  height: 50vh;
  position: fixed;
}

.square__logo {
  border: 2px dashed white;
  width: 50vh;
  height: 50vh;
  position: fixed;
  top:
}

.achievements {
  background-color: pink;
  height: 100vh;
}

<header>
  <div class="logo">
    <div class="circle__logo"><span class="span__logo">my diary</span></div>
    <div class="square__logo"></div>
  </div>
</header>

<section class="achievements">

</section>