details.css

body {
  margin: 0;
  background: url(cake.jpeg);
  padding: 0;
  background-size: cover;
  background-position: center;
  font-family: sans-serif;
}
.singup_box {
  width: 320px;
  height: 450px;
  background: #000;
  color: #fff;
  top: 50%;
  left: 50%;
  position: absolute;
  transform: translate(-50%, -50%);
  box-sizing: border-box;
  padding: 50px;
}
.singup_box h1 {
  margin: 0;
  padding: 0 0 20px;
  text-align: center;
  font-size: 50px;
}
.singup_box p {
  margin: 0;
  padding: 0;
  font-weight: bold;
}
.singup_box input {
  width: 100%;
  margin-bottom: 20px;
}
.singup_box input[type="text"],
input[type="password"],
input[type="number"] {
  border: none;
  border-bottom: 1px solid #fff;
  background: transparent;
  outline: none;
  height: 40px;
  color: #fff;
  font-size: 16px;
}
.singup_box input[type="submit"]:hover {
  cursor: pointer;
  background: #ffc107;
  color: #000;
}
.singup_box input[type="submit"] {
  border: none;
  margin: none;
  background-color: red;
  color: #fff;
  height: 40px;
  border-radius: 20px;
}