style.css

* {
    margin: 0;
    padding: 0;
    font-family: 'Poppins', sans-serif;
    box-sizing: border-box;
}
body{
  background: #001e4d;
}
.app{
  background: #fff;
  width: 90%;
  max-width: 600px;
  margin: 100px auto 0;
  border-radius: 10px;
  padding: 30px;
}
.app h1{
   font-weight: 25px;
   color: #001e4d;
   font-weight: 600;
   border-bottom: 1px solid #333;
   padding-bottom: 38px;
}
.app h1{
   font-size: 25px;
   color: #001e4d;
   font-weight: 600;
   border-bottom: 1px solid #333;
   padding-bottom: 30px;
}
.quiz{
   padding: 20px 0;
}
.quiz h2{
   font-size: 18px;
   color: #001e4d;
   font-weight: 600;
}  
.btn{
   background: #fff;
   color: #222;
   font-weight: 500;
   width: 100%;
   border: 1px solid #222;
   padding: 10px;
   margin: 10px 0;
   text-align: left;
   border-radius: 4px;
   cursor: pointer;
   transition: all 0.3s;
}
.btn:hover:not([disabled]){
   background: #222;
   color: #fff;
}
.btn:disabled{
   cursor: no-drop;
}
#next-btn{
   background: #001e4d;
   color: #fff;
   font-weight: 500;
   width: 150px;
   border: 0;
   padding: 10px;
   margin: 20px auto 0;
   border-radius: 4px;
   cursor: pointer;
   display: none;
}
.correct{
   background: #ffffff;
}
.incorrect{
   background: #ffffff;
}