*{
    padding: 0;
    margin: 0;
}

.wrapper{
    background: url(F.jpg) no-repeat;
    background-size: cover;
    height: 100vh;
}

.navbar{
    height: 80px;
    width: 100%;
    background: rgba(0, 0, 0, 0.4);
}

.logo{
    width: 91px;
    height: 100px;
    padding: 20px;
}

.navbar ul{
    float: right;
    margin-right: 20px;
}

.navbar ul li{
    list-style: none;
    margin: 0 8px;
    display: inline-block;
    line-height: 80px;
}

.navbar ul li a{
    text-decoration: none;
    color: white;
    font-size: 20px;
    padding: 6px 13px;
    font-family: 'Robot', sans-serif;
    transition: .4s;
}

.navbar ul li a.active,
.navbar ul li a:hover{
    background: red;
    border-radius: 2px;
}

.wrapper .center{
    position: absolute;
    top: 60%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-family: sans-serif;
    user-select: none;
}

.jumbotron 
 { 
    width: 60%; 
    margin: auto; 
    text-align: center; 
} 
  
 #output 
{ 
    border: 2px solid black; 
    min-height: 60px; 
    text-align: right; 
    font-weight: bold; 
    font-size: 20px; 
} 
  
.btn 
{ 
    min-width: 120px; 
    border: 2px solid black; 
}