i have a form and inside i have one field and one button. when user hit submit button a php script runs.

in php script i am checking error. ex name is too short etc..

now i want to add a red border only if there is a error. if i get to echo"Error - first name..." than i want to set that input field border red. i am not sure how can i do this. any ideas?


         //check errors
        if((strlen($_POST['f_input']) < 2))
            echo "Error - first name is too short!";

<form action='index.php' method='POST'>
  <input type='field' placeholder='first name'  id='f_field' name='f_input'  />
   <button type="submit" id='button' name="button" >submit</button>

Use css,

   echo"<input type='text' class='abc' value='<?php $_POST['f_input'] ?>'>";

    echo"<input type='text' class='def' value='<?php $_POST['f_input'] ?>'>";

so your css would be like

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