Explanation: The approach may vary depending on your interpretation.... If you have already defined CSS classes, they do not need to be included in the child pages.
Styling with CSS
.Main{ background-color:blue; }
Applying the Style to a Normal Page
<body class="Main">
....
</body>
Excluding the CSS Class from Other Pages
<body>
.....
</body>
If you have applied styles to specific selectors, you will need to override them in child pages as shown below
Adjusted CSS Code for Specific Styling
body{ background-color:blue; }
Child Page where different styling is required
<style type="text/css">
body {background-color:green;}
</style>
</head>
<body>
......
</body>