style.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body { 
  background-image: url('key.jpg');
  background-position: center center; 
  background-size: 100% 100%; 
} 

.main {
  width: 80vw;
  margin: auto;
  display: flex;
  justify-content: center;
}

.titulo {
  padding: 15px;
  width: 30vw;
  margin: auto;

}

.box {
  padding: 10px;
  margin: 0 10px 0 10px;
  box-shadow: 2px 2px 2px 1px rgba(0, 0, 0, 0.2);
  background-color: rgb(109, 103, 103);
  border-radius: 0.5em;
  width: 30vw;
  height: auto;
}

.btn {
  border: 0;
  color: white;
  font-weight: bold;
  background-color: blue;
  padding: 10px;
  margin-top: 10px;
  border-radius: 0.5em;
}

.text-input {
  border-radius: 0.5em;
  border: 1px solid rgba(0, 0, 0, 0.2);
  display: block;
  padding: 0.5em;
  width: 100%;
  height: 50px;
}

footer {
  text-align: center;
  margin-top: 8vh;
  margin-bottom: 10px;
  width: 100%;
  color: black;
}