<> one , First, the final effect :
 <> two , code 
 General structure diagram :
 <>1,index.html
<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <title>Login</title> <
link rel="stylesheet"href="./css/style.css" /> </head> <body> <form class="box" 
action="index.html"method="post"> <h1>Login</h1> <input type="text"name=""
placeholder="UserName" /> <input type="password"name=""placeholder=
"UserPassword" /> <input type="submit" name="" value="Login" /> </form> </body> 
</html> 
 <>2,style.css
body{ margin: 0; padding: 0; background-image: url(../img/ Bridge .jpg); 
background-repeat: no-repeat; background-size:100%; background-position: 0px 
-50px; } .box{ width: 300px; padding: 40px; position: absolute; top: 50%; left: 
50%; transform: translate(-50%,-50%); background-color: #00000068; text-align: 
center; } .box input[type = "text"],.box input[type = "password"]{ border: 0; 
background: none; display: block; margin: 20px auto; text-align: center; border:
 2px solid #c8d6e5; padding: 14px 10px; outline: none; color: #ffffff; 
border-radius: 24px; transition: 0.25s; } h1{ color: #FFFFFF; text-transform: 
uppercase; font-weight: 500; } .box input[type = "text"]:focus, .box input[type 
= "password"]:focus{ width: 280px; border-color: #FFFFFF; } .box input[type = 
"submit"]{ border: 0; font-size: 17px; background: none; display: block; margin:
 20px auto; text-align: center; border: 2px solid #FFFFFF; padding: 14px 40px; 
outline: none; color: #ffffff; border-radius: 24px; transition: 0.25s; cursor: 
pointer; } .box input[type = "submit"]:hover{ background-image: linear-gradient(
120deg, #e0c3fc 0%, #8ec5fc 100%); font-size: x-large; } 
 <>3, Background picture taken by yourself 
  Hope to help more friends ~~~~~~~~~
Technology