效果如图：
完整代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>表单</title>
<style type="text/css">
.input-field, .input-field * {
-webkit-box-sizing: border-box;
box-sizing:border-box;
}
.input-field {
position: relative;
width: 200px;
margin: 20px 50px;
}
.input-field input {
background-color: transparent;
border: none;
border-radius: 0;
height: 35px;
width: 100%;
padding: 0;
box-shadow: none;
outline: none;
-webkit-transition: all 0.3s;
transition: all 0.3s;
}
.input-field input+span {
position: absolute;
top: 100%;
left: 0;
display: inline-block;
max-width: 100%;
z-index: 0;
width: 100%;
height: 1px;
border-bottom: 1px solid #d9d9d9;
}
.input-field span:after {
content: "";
position: absolute;
bottom: 0;
left: 0;
width: 100%;
height: 2px;
background: #2196f3;
-webkit-transform: scale(0);
transform: scale(0);
-webkit-transition: all .2s ease-out;
transition: all .2s ease-out;
}
.input-field input:focus+span:after {
-webkit-transform: scale(1);
transform: scale(1);
}
.input-field.input-field-icon i {
position:absolute;
right:0;
top:50%;
padding:0 5px;
font-size:1.5em;
-webkit-transform: translate(0, -50%);
transform: translate(0, -50%);
}
.input-field.input-field-icon input {
padding-right:30px;
}
.input-field.success input+span {
border-color: #b5dfb7;
}
.input-field.warning input+span {
border-color: #ffd699;
}
.input-field.error input+span {
border-color: #fccbc7;
}
.input-field.success span:after {
background:#4caf50;
}
.input-field.warning span:after {
background:#ffc107;
}
.input-field.error span:after {
background:#f44336;
}
.input-field.input-field-icon.success i {
color: #4caf50;
}
.input-field.input-field-icon.warning i {
color: #ffc107;
}
.input-field.input-field-icon.error i {
color: #f44336;
}
.input-field.linear span:after {
background:-webkit-linear-gradient(left, #8C0044 20%, #00FFFF 50%, #7700FF 80%);
}
</style>
</head><body>
<div class="input-field">
<input id="last_name" type="text" placeholder="账号">
<span></span> </div>
<div class="input-field success input-field-icon">
<input id="last_name" type="text" placeholder="账号">
<span></span> <i class="ion-android-done"></i> </div>
<div class="input-field warning input-field-icon">
<input id="last_name" type="text" placeholder="账号">
<span></span> <i class="ion-alert-circled"></i> </div>
<div class="input-field error input-field-icon">
<input id="last_name" type="text" placeholder="账号">
<span></span> <i class="ion-android-close"></i> </div>
<div class="input-field linear">
<input id="last_name" type="text" placeholder="账号">
<span></span> </div>
</body>
</html>
