div {
border-width: medium;
padding: 5px;
margin: 5px 10px;
border-style: solid;
}
.ex1 {border-width: thin;}
.ex2 {border-width: medium;}
.ex3 {border-width: thick;}
.ex4 {border-width: 10px;}
.ex5 {border-width: 10px 5px;}
.ex6 {border-width: 10px 5px 15px;}
.ex7 {border-width: 10px 5px 15px 40px;}
<!DOCTYPE html>
<html lang="ko">
<head></head>
<body>
<div class="ex1">border-width: thin</div>
<div class="ex2">border-width: medium</div>
<div class="ex3">border-width: thick</div>
<div class="ex4">border-width: 10px;</div>
<div class="ex5">border-width: 10px 5px;</div>
<div class="ex6">border-width: 10px 5px 15px;</div>
<div class="ex7">border-width: 10px 5px 15px 40px;</div>
</body>
</html>