それを自分で試してみてください - CSS ex_pagination_border

<!DOCTYPE html>
<html>
<head>
<style>
ul.pagination {
    display: inline-block;
    padding: 0;
    margin: 0;
}

ul.pagination li {display: inline;}

ul.pagination li a {
    color: black;
    float: left;
    padding: 8px 16px;
    text-decoration: none;
    transition: background-color .3s;
    border: 1px solid #ddd;
}

.pagination li:first-child a {
    border-top-left-radius: 5px;
    border-bottom-left-radius: 5px;
}

.pagination li:last-child a {
    border-top-right-radius: 5px;
    border-bottom-right-radius: 5px;
}

ul.pagination li a.active {
    background-color: #4CAF50;
    color: white;
    border: 1px solid #4CAF50;
}

ul.pagination li a:hover:not(.active) {background-color: #ddd;}
</style>
</head>
<body>

<h2>Pagination with Rounded Borders</h2>
<ul class="pagination">
  <li><a href="#">«</a></li>
  <li><a href="#">1</a></li>
  <li><a class="active" href="#">2</a></li>
  <li><a href="#">3</a></li>
  <li><a href="#">4</a></li>
  <li><a href="#">5</a></li>
  <li><a href="#">6</a></li>
  <li><a href="#">7</a></li>
  <li><a href="#">»</a></li>
</ul>

</body>
</html>