style.css

@import "https://fonts.googleapis.com/css?family=Ubuntu";

body
{
height: 100vh;
font-family: 'Ubuntu', sans-serif;
background: rgb(34,193,195);

}

.titulo
{
text-align: center;
color: #ffffff;
}

.principal
{
  text-align: center;
  color: #ffffff;
  border-radius: 15px;
  width: 500px;
  margin: 0 auto;
  background-color: #0080FF;
  padding: 20px 0px;
}
input[type=number]{
  width: 85%;
  padding: 12px 20px;
  margin: 15px 0;
  display: inline-block;
  border: 1px solid #ccc;
  border-radius: 4px;
  box-sizing: border-box;
}

.botones{
  width: 40%;
  background-color: #043646;
  color: #fff;
  padding: 14px 20px;
  margin: 8px 0;
  border: none;
  border-radius: 10px;
  cursor: pointer;
  font-weight: bold;
  font-size: 1.2em;
}


.botones:hover {
  background-color: #081624;
}

.resultado{
    color: #333;
    width: 50%;
    margin: 0 auto;
    display: none;
}
.resultado h3{
  text-align: left;
  color: #fff;
}

.content{
  display: flex;
  flex-direction: column;
  align-items: center;
  color: #fff;
}
.content span{
  margin-right: auto;
  padding: 6px;

}