style.css

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

body {
  background-image:url(https://blog.powerdata.es/hs-fs/hubfs/iStock_000063192435_Small.jpg?width=700&name=iStock_000063192435_Small.jpg);
  font-family: sans-serif;
}

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

.titulo {
  color: bisque;
  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: white;
  border-radius: 0.5em;
  width: 30vw;
  height: 15vw;
}

.btn {
  border: 0;
  color: white;
  font-weight: bold;
  background-color: blue;
  padding: 10px;
  margin-top: 15px;
  border-radius: 0.5em;
  position :static;
  left: 200px;
  top: 200px;
}

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

.invisible{
  display:none;
}

#error-texto{
 
  
  border-color: black;
  
  color:red;
}
.realizado{
  background-color: blue;
  color:cornsilk;
  text-align: center;
  width: 100%;
  max-width: 100%;
  position:fixed;
  bottom: 0;
}