html - CSS Form下划线文本域动画效果

Question

我的表单部分有以下代码(下图)，我希望在其中(下图)在文本输入字段中完成下划线动画。每当用户将注意力集中在该字段上时，动画就会完成。动画要流畅自如。

但是我找不到其中缺少的东西。出了什么问题以及如何解决？任何人请帮助

html {
  -moz-osx-font-smoothing: grayscale;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizelegibility;
}

html, body {
  height: 100%;
}
#contact {
  font-family: "Montserrat", sans-serif;
  font-size: 14px;
  font-weight: 300;
  letter-spacing: 3px;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -ms-flex-flow: row wrap;
      flex-flow: row wrap;
  margin: 10% 0;
}
#contact main, body footer {
  width: 100%;
}
#contact main {
  height: 100%;
  -webkit-box-align: center;
      -ms-flex-align: center;
          align-items: center;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
}

.form .text-input, .form .textarea, .form .label, .form .button {
  padding: 1em 1.5em;
  -webkit-appearance: none;
     -moz-appearance: none;
          appearance: none;
  outline: none;
  line-height: normal;
  border: 1px solid transparent;
  border-radius: 0;
}

.form .text-input, .form .textarea {
  font: inherit;
  line-height: normal;
  width: 100%;
  box-sizing: border-box;
  display: block;
  padding-left: 0;
  border-bottom-color: #00d2ff;
  background: transparent;
  outline: none;
  color: black;
}
.form .text-input:placeholder, .form .textarea:placeholder {
  color: rgba(0, 0, 0, 0.7);
}
.form .text-input:-webkit-autofill, .form .textarea:-webkit-autofill {
  box-shadow: 0 0 0px 1000px white inset;
  border-top-color: white;
  border-left-color: white;
  border-right-color: white;
}
.form .error.text-input, .form .error.textarea, .error .form .text-input, .form .error .text-input, .error .form .textarea, .form .error .textarea {
  border-color: transparent transparent red transparent;
}
.form:not(.has-floated-label) .text-input:active, .form:not(.has-floated-label) .textarea:active, .form:not(.has-floated-label) .text-input:focus, .form:not(.has-floated-label) .textarea:focus {
  border-color: transparent transparent black transparent;
}

.form .label {
  position: absolute;
  z-index: 10;
  pointer-events: none;
  padding-left: 0;
}

.form .label {
  top: 0;
  left: 0;
  color: rgba(0, 0, 0, 0.3);
  -webkit-transition: color 0.3s;
  transition: color 0.3s;
}
.active .form .label, .form .active .label {
  font-size: 0.80em;
  line-height: 1;
  font-weight: 600;
  text-transform: uppercase;
  padding: 0;
  color: rgba(0, 0, 0, 0.7);
  background: white;
}
.focus .form .label, .form .focus .label {
  color: black;
}

.form.has-floated-label .field:after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0%;
  border-bottom: 3px solid #00d2ff;
  -webkit-transition: width 0.3s cubic-bezier(0.455, 0.03, 0.515, 0.955);
  transition: width 0.3s cubic-bezier(0.455, 0.03, 0.515, 0.955);
}

.form.has-floated-label .field.focus:after {
  width: 100%;
}

.form .button {
  font: inherit;
  line-height: normal;
  cursor: pointer;
  background-color: #00d2ff;
  color: white;
  text-transform: uppercase;
  text-align: center;
  letter-spacing: 0.14286em;
  transition-duration: 0.4s;
}
.form .button:hover, .form .button:focus, .form .button:active {
  box-shadow: 0 10px 15px rgba(0, 0, 0, .1);
}
.form .button:active {
  position: relative;
  top: 1px;
  left: 1px;
}

.form {
/*  max-width: 50em; */
  width: 100%;
  margin: 0 10%;
/*  padding: 1em 2em;  */
  box-sizing: border-box;
  overflow: hidden;
}
.form .field {
  position: relative;
  width: 100%;
  margin-bottom: 1.5em;
  float: left;
  
}
@media screen and (min-width: 40em) {
  .form .field.half {
    width: calc(50% - 2em);
    margin-right: 2em;
  }
  .form .field.half + .half {
    margin-left: 2em;
    margin-right: 0;
  }
}
.form .field:last-child {
  float: right;
  width: auto;
}
.form .textarea {
  max-width: 100%;
}

<section id="contact">
<main>  
  <form action='' class='form'>
    
    <p class='field required half'>
      <label class='label required' for='name'>Name</label>
      <input class='text-input' id='name' name='name' required type='text'>
    </p>
    <p class='field required half'>
      <label class='label' for='email'>E-mail</label>
      <input class='text-input' id='email' name='email' required type='email'>
    </p>
    <p class='field'>
      <label class='label' for='message'>Message</label>
      <textarea class='textarea' cols='50' id='message' name='message' required rows='4'></textarea>
    </p>
    <p class='field'>
      <input class='button' type='submit' value='Send message'>
    </p>
  </form>
</main>
  </section>

Answer 1

这是一个例子:

.input-name{
  position: relative;
  display: inline-block;
  overflow: hidden;
}
.input-name > input[type=text]{
  border: none;
  border-bottom: 2px solid red;
  outline: none;
}

.underline-animation{
  transition: all 0.5s;
  display: inline-block;
  bottom: 0;
  left: -100%;
  position: absolute;
  width: 100%;
  height: 2px;
  background-color: #64e4fe;
}
.input-name > input[type=text]:focus + .underline-animation{
  left: 0;
}

 <div class="input-name">
  <input type="text" placeholder="name">
  <span class="underline-animation"></span>
</div>