You don't really need flex box to do this, but heres a close representation to what you're looking for. You'll have to change the font family as well
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Bradey Whitlock</title>
</head>
<body style="margin: 0px">
<div style="background-color:#28AF42; height: 50px; display: flex; align-items: center; justify-content: space-around; font-family: monospace">
<div style="color: white; font-size: 25px">edibit</div>
<div style="display: flex; justify-content: space-around">
<div style="background-color:#28AF42; border: 1px solid white; border-radius: 3px; padding: 3px 15px; color: white; margin-right: 20px; cursor: pointer">Sign In</div>
<div style="background-color:#28AF42; border: 1px solid white; border-radius: 3px; padding: 3px 15px; color: white; cursor: pointer">Register</div>
</div>
</div>
</body>
</html>