:root{
   --primary-dark : black;
   --primary-green : green;
}

body{
    background-color: gray;
    color: var(--primary-dark);
}
h1{
    text-align: center;
}
label{
    text-align: center;
}
#output-box{
    text-align: center;
    margin: 1rem;
    border-radius: 0.5rem;
   
}

.container{
    width: 50%;
  margin: auto;
}

input,label{
    display: block;
    border-radius: 0.5rem;
    padding: 0.5rem;
}

input{
    margin-bottom: 1rem;
    width: 100%;
    font-weight: bold;
    font-size: larger;
}

#check-number{
    display: block;
    margin-top: 1rem;
    margin: auto;
    border-radius: 0.5rem;
    padding: 0.5rem;
}