使用CSS：enabled选择器为每个启用的<input>元素设置样式。您可以尝试运行以下代码来实现：enabled选择器-
<!DOCTYPE html>
<html>
<head>
<style>
input:enabled {
background: blue;
}
</style>
</head>
<body>
<form action = "">
Subject <input type = "text" name = "subject"><br>
Student: <input type = "text" name = "student"><br>
Age: <input type = "number" name = "age" disabled><br>
</form>
</body>
</html>