以下是一个简单的登录页面的HTML/CSS/JavaScript代码：
HTML代码：
```
<!DOCTYPE html>
<html>
<head>
<title>Login Page</title>
<link rel="stylesheet" type="text/css" href="style.css">
</head>
<body>
<div class="login-box">
<h2>Login</h2>
<form>
<div class="user-box">
<input type="text" name="username" required="">
<label>Username</label>
</div>
<div class="user-box">
<input type="password" name="password" required="">
<label>Password</label>
</div>
<a href="#">
<span></span>
<span></span>
<span></span>
<span></span>
<input type="submit" value="Login">
</a>
</form>
</div>
</body>
</html>
```
CSS代码：
```
* {
margin: 0;
padding: 0;
box-sizing: border-box;
}
body {
background: #34495e;
font-family: sans-serif;
}
.login-box {
width: 280px;
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
background: #191919;
padding: 40px;
border-radius: 10px;
box-shadow: 0 0 20px 0px #000;
}
.login-box h2 {
color: #fff;
text-align: center;
margin-bottom: 30px;
}
.user-box {
position: relative;
}
.user-box input {
width: 100%;
padding: 10px 0;
font-size: 16px;
color: #fff;
margin-bottom: 30px;
border: none;
border-bottom: 1px solid #fff;
outline: none;
background: transparent;
}
.user-box label {
position: absolute;
top: 0;
left: 0;
padding: 10px 0;
font-size: 16px;
color: #fff;
pointer-events: none;
transition: 0.5s;
}
.user-box input:focus ~ label,
.user-box input:valid ~ label {
top: -20px;
left: 0;
color: #03a9f4;
font-size: 12px;
}
.login-box a {
position: relative;
display: inline-block;
padding: 10px 20px;
color: #03a9f4;
font-size: 16px;
text-decoration: none;
text-transform: uppercase;
overflow: hidden;
transition: 0.5s;
margin-top: 40px;
letter-spacing: 4px;
}
.login-box a:hover {
background: #03a9f4;
color: #fff;
border-radius: 5px;
box-shadow: 0 0 5px #03a9f4,
0 0 25px #03a9f4,
0 0 50px #03a9f4,
0 0 100px #03a9f4;
}
.login-box a span {
position: absolute;
display: block;
}
.login-box a span:nth-child(1) {
top: 0;
left: -100%;
width: 100%;
height: 2px;
background: linear-gradient(90deg, transparent, #03a9f4);
animation: animate1 1s linear infinite;
}
@keyframes animate1 {
0% {
left: -100%;
}
50%,100% {
left: 100%;
}
}
.login-box a span:nth-child(2) {
top: -100%;
right: 0;
width: 2px;
height: 100%;
background: linear-gradient(180deg, transparent, #03a9f4);
animation: animate2 1s linear infinite;
animation-delay: 0.25s;
}
@keyframes animate2 {
0% {
top: -100%;
}
50%,100% {
top: 100%;
}
}
.login-box a span:nth-child(3) {
bottom: 0;
right: -100%;
width: 100%;
height: 2px;
background: linear-gradient(270deg, transparent, #03a9f4);
animation: animate3 1s linear infinite;
animation-delay: 0.5s;
}
@keyframes animate3 {
0% {
right: -100%;
}
50%,100% {
right: 100%;
}
}
.login-box a span:nth-child(4) {
bottom: -100%;
left: 0;
width: 2px;
height: 100%;
background: linear-gradient(360deg, transparent, #03a9f4);
animation: animate4 1s linear infinite;
animation-delay: 0.75s;
}
@keyframes animate4 {
0% {
bottom: -100%;
}
50%,100% {
bottom: 100%;
}
}
```
JavaScript代码：
```
// 获取所有的输入框
const inputs = document.querySelectorAll(".user-box input");
// 给每个输入框添加事件监听器
inputs.forEach(input => {
input.addEventListener("focus", function() {
this.parentNode.classList.add("active");
});
input.addEventListener("blur", function() {
if (this.value === "") {
this.parentNode.classList.remove("active");
}
});
});
```效果图如下：
