单击输入时更改字体真棒图标颜色

Question

我想在点击输入字段时更改字体真棒图标的颜色。到目前为止，我只设法在单击时更改输入边框颜色，但不知道如何更改图标。不知道为什么input:focus i 不起作用。我也试过input:focus .fa，但什么也没有。任何建议将不胜感激，谢谢！

* {
    margin: 0;
    padding: 0;
    outline: 0;
    box-sizing: border-box;
}

#signInForm .input-icons {
    position: relative;
    display: inline-block;
}

#signInForm .input-icons input {
    width: 300px;
    font-size: .9rem;
    text-indent: 20px;
    padding: .1rem;
    border: 0;
    border-bottom: solid 2px #999;
    background-color: transparent;
}

#signInForm .input-icons i {
    color: #999;
    position: absolute;
    top: .15rem;
    left: .3rem;
}

#signInForm .input-icons input:focus {
    border-color: #00aef0;
}

#signInForm .input-icons input:focus i {
    color: #00aef0;
}

<!-- Font Awesome CDN -->
    <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.0.12/css/all.css" integrity="sha384-G0fIWCsCzJIMAVNQPfjH08cyYaUtMwjJwqiRKxxE/rx96Uroj1BtIQ6MLJuheaO9" crossorigin="anonymous">
    
<div id="signInForm">
  <form>
    <div class="input-icons">
      <i class="fas fa-user"></i>
      <input type="text" placeholder="Name" required>
    </div>
    <div class="input-icons">
      <i class="fas fa-lock"></i>
      <input type="password" placeholder="Password" required>
    </div>
  </form>
</div>

Answer 1

由于您的元素有position:absolute，并且没有先前的选择器，您可以更改图标使其在输入之后并能够使用+ selector：

* {
    margin: 0;
    padding: 0;
    outline: 0;
    box-sizing: border-box;
}

#signInForm .input-icons {
    position: relative;
    display: inline-block;
}

#signInForm .input-icons input {
    width: 300px;
    font-size: .9rem;
    text-indent: 20px;
    padding: .1rem;
    border: 0;
    border-bottom: solid 2px #999;
    background-color: transparent;
}

#signInForm .input-icons i {
    color: #999;
    position: absolute;
    top: .15rem;
    left: .3rem;
}

#signInForm .input-icons input:focus {
    border-color: #00aef0;
}

#signInForm .input-icons input:focus + i {
    color: #00aef0;
}

<!-- Font Awesome CDN -->
    <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.0.12/css/all.css" integrity="sha384-G0fIWCsCzJIMAVNQPfjH08cyYaUtMwjJwqiRKxxE/rx96Uroj1BtIQ6MLJuheaO9" crossorigin="anonymous">
    
<div id="signInForm">
  <form>
    <div class="input-icons">
      <input type="text" placeholder="Name" required>
      <i class="fas fa-user"></i>
    </div>
    <div class="input-icons">
      <input type="password" placeholder="Password" required>
      <i class="fas fa-lock"></i>
    </div>
  </form>
</div>