body{
    background-size: cover;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell,'Open Sans','Helvetica Neue',sans-serif;
    font-weight: bold;
    text-align: center;
}

nav{
    position: relative;
    display: flex;
    align-items: center;
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}

#check{
    display: none;
}

nav ul{
    position: fixed;
    left: 15px;
    top: 0;
    width: 150px;
    height: 100vh;
    background: none;
    list-style: none;
    padding-top: 50px;
    margin: 0;
    transform: translateX(-150%);
    transition: transform 0.3s ease-in-out;
    z-index: 999;
}

#check:checked ~ ul{
    transform: translateX(-30%);
}

nav ul li{
    line-height: 40px;
    margin: 0;
    width: 100%;
    list-style: none;
}

nav ul li a{
    text-decoration: none;
    color: black;
    font-size: 16px;
    padding: 0 20px;
    display: block;
    transition: background 0.3s ease;
}

nav ul li a:hover{
    color: #667eea;
}

a.active{
    background-color: rgba(255, 255, 255, 0.2);
    border-left: 4px solid white;
}

.checkbtn{
    font-size: 28px;
    color: #333;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 10px;
    position: relative;
    z-index: 1000;
    margin-right: 20px;
    transition: color 0.3s ease;
}

.checkbtn p{
    margin: 0;
    font-size: 18px;
    font-weight: bold;
}

.checkbtn:hover{
    color: #667eea;
}

h1{
    margin-top: 10px;
    margin-bottom: 10px;
}

h2{
    font-size: 50px;
    margin-top: 0px;
    margin-bottom: 20px;
}

button{
    border: none;
    padding-top: 10px;
    padding-bottom: 10px;
    color:white;
    font-weight: bold;
    width: 120px;
    margin-bottom: 5px;
    border-radius: 5px;
}

form{
    display: flex;
    flex-direction: column;
    align-items: left;
    justify-content: center;
    padding-top: 50px;
}

label{
    font-size: 15px;
    margin-bottom: 5px;
    text-align: left;
}   

input{
    width: 60px;
    height: 25px;
    border-radius: 5px;
    border: 2px solid black;
    text-align: center;
    font-size: 20px;
    margin-bottom: 10px;
}

footer{
    margin-top: 20px;
    font-size: 12px;
    color: gray;
}

#showAnswers-btn{
    background: darkred;
}

#submit-btn{
    background: darkgreen;
}

#reset-btn{
    background: darkblue;
}

#next-btn{
    background: darkorange;
}

/* responsive button layout */
.button-group {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 10px;
}

.button-group button {
    flex: 1 1 45%;
    max-width: 150px;
}