index.css

*{
    margin:0;
    padding:0;
    font-family: 'poppins', sans-serif;
    box-sizing:border-box;
}

body{
    width:100%;
    height:100%;
    background-image: url(img.png);
}

.app{
    background: white;
    width: 90%;
    max-width:600px;
    margin: 100px auto 0;
    border-radius: 30px;
    padding: 30px;
}

.app h1{
    font-size:38px;
    color: #001e4d;
    font-weight:600;
    border-bottom: 2px solid #333;
    padding-bottom: 20px;
}

.quiz{
    padding:20px 0;
}

.quiz h2{
    font-size:18px;
    color: #001e4d;
    font-weight:600;
}

#question{
    font-size: 1.2em;
    font-weight: 700;
    font-family: Verdana, Geneva, Tahoma, sans-serif;
    margin-bottom:15px;
}

.btn{
    background: #fff;
    color:#2d2929;
    font-weight:600;
    font-size: 1.2rem;
    font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
    width:100%;
    border:1px solid #222;
    padding: 10px;
    margin: 10px 0;
    text-align: left;
    border-radius: 50px;
    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:700;
    font-size:large;
    width:150px;
    border:0;
    padding:10px;
    margin:20px auto 0;
    border-radius: 8px;
    cursor: pointer;
    display:none;
}

.correct{
    background: #199850;
}

.incorrect{
    background: #d26666;
}