Warum gekomme ich Scrollbars, wenn ich hinter dem Body-Bereich <form> einfüge, aber nicht wenn ich es hinter <header> und <main> einfüge 
Ist das bei euch auch so!
HTML
<!DOCTYPE html>
<html>
<head>
<title>HOMEPAGE</title>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<meta charset="UTF-8">
<style>
* {
margin: 0;
padding: 0;
box-sizing:border-box;
}
body {
padding:0;
display: flex;
flex-direction: column;
width: 100vw;
height: 100vh;
justify-content: space-between;
background: lightgreen;
}
header h2 , header nav {
text-align:center;
}
main {
display:flex;
height:100vh;
overflow:hidden;
}
.dropdown , .status , .output , .file , footer , nav , h2 {
margin:0 0 5px 0;
border:1px solid #000;
background:#fff;
}
.left , .right {
display:flex;
justify-content: space-between;
flex-direction: column;
}
.left {
margin-right:5px;
width: auto;
}
.right {
width:100vw;
overflow:hidden;
}
.file , .output {
overflow:auto;
display:flex;
height:100vh;
}
.file , .dropdown , .status {
white-space:nowrap;
}
.output {
white-space:pre;
}
.output {
padding:0;
background: lightgreen;
}
.output div {
padding:0;
background:#fff;
}
.output p {
background:#fff;
}
</style>
</head>
<body>
<FORM target="_self" action="" method="post">
<header>
<nav>
<p> HEADLINE </p>
</nav>
</header>
<main>
<p> TEXT1 </p>
</main>
</FORM>
</body>
</html>
.