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Does ID have to be unique in the whole HTML page?
Yes, IDs must be unique in the entire HTML page. Even the official HTML standards suggest the same −
Unique IDs with the id attribute
Example
Let us see an example. Here, we have used the id attribute −
<!DOCTYPE html> <html> <head> <style> #myHeader { border: 2px solid yellow; background-color: orange; padding: 50px; text-align: center; } </style> </head> <body> <h1 id="myHeader"> Demo Heading </h1> <p>This is a text outside.</p> </body> </html>
Output
Displaying four different unique IDs
Another example displaying four different unique IDs −
<!DOCTYPE html> <html> <head> <style> #container { width: 100%; font-size: 10px; text-align: center; } #left { float: left; width: 100px; border: 2px solid green; } #right { float: right; width: 100px; border: 2px solid orange; } #center { margin: 0 auto; width: 100px; border: 2px solid red; } </style> </head> <body> <div id="container"> <div id="left"> <h1>Left</h1> </div> <div id="right"> <h1>Right</h1> </div> <div id="center"> <h1>Center</h1> </div> </div> </body> </html>
Output
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