Свойство border-left

border-left: border-left-width || border-left-style || border-left-color

<!DOCTYPE html>
<html lang='ru'>
<head>
<meta charset='UTF-8'>
<meta name='viewport' content='width=device-width, initial-scale=1.0'>
<title>Document</title>
</head>
<body>
<style>
#border {
width: 200px;
height: 100px;
border: 5px dashed rgb(10, 238, 246);
border-left: 5px dotted lightgreen;
}
</style>
<div id='border'></div>
</body>
</html>