My first game ever

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>لعبة قطرات الماء</title>
    <link rel="stylesheet" href="styles.css">
</head>
<body>
    <div id="game">
        <h1>لعبة قطرات الماء</h1>
        <div id="stage"></div>
        <button id="nextStage" onclick="nextStage()">المرحلة التالية</button>
    </div>
    <script src="game.js"></script>
</body>
</html>

I’ve edited your code for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.

You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.

See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (').

Salam and Marhaban!

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