<header>
  <div class='some-stuff'></div>
  <div class='auth-block'>
    <button>LOG IN</button>
    <button>SIGN UP</button>
  </div>
</header>

* {
  margin: 0;
}

header {
  width: 100vw;
  height: 60px;
  background-color: grey;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.auth-block {
  margin-right: 20px;
}

.auth-block button {
  padding: 5px 20px;
  font-size: 14px;
  font-weight: bold;
  cursor: pointer;
}

.auth-block button:last-of-type {
  background-color: orange;
  border: 1px solid white;
  color: white;
}