Check out example codes for "css priority rules". It will help you in understanding the concepts better.

Code Example 1

/* CSS Hierarchy: You can apply a global CSS rule and, using internal or 
inline CSS, cause particular changes to each html page */

/* Highest priority to lowest priority: */

/* 1º - Inline CSS */
<body style="background-color: green;">
...
</body>


/* 2º - Internal CSS */
<head>
	<style>
		body {
      		background-color: blue;
		}
	</style>
</head>


/* 3º - External CSS with id or class selectors */

.name_of_class {
  color: #5c8d89;
}

#name_of_id {
  font-size: 30px;
}


/* 4º - External CSS with tag selectors */
body {
  background-color: red;
}

h1 {
  color: #74b49b;
}

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