无法获得标签和输入以进行焦点工作

Question

我想把标签放在输入的顶部。但是当我在代码中移动它时，CSS Focus样式停止工作。在焦点上，标签需求变得更大。如何解决这个问题？尝试了一切...

＆＃13;

＆＃13;

form {
  margin-top: 25px;
}

input {
  
  display:block;
}

form input:focus + label {
  font-size: 1.5em;
}

＆＃13;

<form>
  
    <!-- DOESN'T WORK
=====================
-->
  <label for="firstname">First name:</label>
  <input id="firstname" name="firstname" type="text">

  <br>
  
  <!-- WORKS 
=====================
-->
  <input id="lasttname" name="firstname" type="text">
  <label for="lasttname">Last name:</label>


</form>

＆＃13;

＆＃13;

＆＃13;

Answer 1

jQuery解决方案。

$(function() {
  $('form input[type="text"]').focus(function() {
    $(this).prev('label').css("font-size", "1.5em");
  });
  $('form input[type="text"]').focusout(function() {
    $(this).prev('label').css("font-size", "1em");
  });
});

form {
  margin-top: 25px;
}
form input:focus + label {
  font-size: 1.5em;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form>

  <!-- DOESN'T WORK
=====================
-->
  <label for="firstname">First name:</label>
  <input id="firstname" name="firstname" type="text">

  <!-- WORKS 
=====================
-->
  <input id="lasttname" name="firstname" type="text">
  <label for="lasttname">Last name:</label>


</form>

Answer 2

尝试在额外div中包装标签和输入，并使用flex-box：

＆＃13;

＆＃13;

form {
  margin-top: 25px;
}
form input:focus + label {
  font-size: 1.5em;
}

.form-row {
  display: flex;
  flex-direction: column;
  
  margin-bottom: 8px;
}

.form-row label {
   order: 1;
}

.form-row input {
   order: 2; 
   width: 141px;
}

＆＃13;

<form>
  
    <!-- DOESN'T WORK
=====================
-->
  <div class='form-row'>
    <input id="firstname" name="firstname" type="text">
    <label for="firstname">First name:</label>
  </div>

  <!-- WORKS 
=====================
-->
  <input id="lasttname" name="firstname" type="text">
  <label for="lasttname">Last name:</label>


</form>

＆＃13;

＆＃13;

＆＃13;