要在单个声明中设置所有左边框属性，请使用borderLeft属性。您可以尝试运行以下代码以了解如何设置左边框属性-
<!DOCTYPE html>
<html>
<head>
<style>
#box {
border: thick solid gray;
width: 300px;
height: 200px
}
</style>
</head>
<body>
<div id = "box">Demo Text</div>
<br>
<br>
<button type = "button" onclick = "display()">Change left border</button>
<script>
function display() {
document.getElementById("box").style.borderLeft = "thick solid #000000";
}
</script>
</body>
</html>