Untitled

HTML:
<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Box-Modell erkunden</title>
    <link href="css-box-modell.css" rel="stylesheet">
</head>
<body>

<div id="bereich">
    Beschreibung der CSS-Eigenschaften
</div>

</body>
</html>
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CSS
#bereich {
    background-color: yellow;
    width: 400px;
    padding: 10px;
    margin: 15px;
    border-top: 3px green solid;
    border-right: 2px red hidden;
    border-bottom: 2px black dashed;
    border-left: 12px red double;
}