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<form action="" method="post">
Đăng ký học:<br>
HTML <input type="checkbox" name="check_html">, CSS <input type="checkbox" name="check_css" value="CSS"><br>
<button type="submit">Gửi</button>
</form>
<?php if(isset($_POST["check_html"])) { echo $_POST["check_html"]; } ?>
<?php if(isset($_POST["check_css"])) { echo $_POST["check_css"]; } ?>