when adding a block, the header goes down

Question

I have such a problem, I made the header of the site and now, after adding the blocks, the header goes out.

When I add a block and set its location on the site, the header leaves along with the block at this location, I need only the block to leave, and the header remains in place

* {
  padding: 0;
  margin: 0;
  font-family: "Roboto";
}

body {
  background-color: #1F1E1E;
}

ul.hr li {
  display: inline;
  margin-right: 170px;
  padding: 3px;
}

.logo {
  color: white;
  background-color: #FF8616;
  border-radius: 10px;
  width: 10%;
  text-align: center;
  margin-top: 20px;
  margin-left: 70px;
  font-size: 50px;
}

.menu {
  margin-left: 800px;
  margin-top: -55px;
  color: white;
  font-size: 30px;
}

.header {
  background-color: #4f4d4d;
  position: fixed;
  width: 1920px;
  height: 100px;
}

.sell {
  margin-top: 100px;
}

<link rel="preconnect" href="https://fonts.googleapis.com">
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
<link href="https://fonts.googleapis.com/css2?family=Roboto:wght@500&display=swap" rel="stylesheet">
<meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<header>
  <div class="header">
    <div class="logo">
      <span>
                STORE
            </span>
    </div>
    <div class="menu">
      <ul class="hr">
        <li>
          Регистрация
        </li>
        <li>
          Авторизация
        </li>
      </ul>
    </div>
  </div>
</header>

<div class="sell">
  <ul>
    <li>
      ★ Brawl Stars
    </li>
    <li>
      ★ Minecraft
    </li>
    <li>
      ★ Standoff
    </li>
    <li>
      ★ Genshin
    </li>
  </ul>
</div>