div {
border-width: medium;
padding: 5px;
margin: 5px 10px;
}
.ex1 {border: 5px solid red;}
.ex2 {border: 4px dotted blue;}
.ex3 {border: double;}
<!DOCTYPE html>
<html lang="ko">
<head></head>
<body>
<div class="ex1">border: 5px solid red;</div>
<div class="ex2">border: 4px dotted blue;</div>
<div class="ex3">border: double;</div>
</body>
</html>