style.css

*, *::before, *::after{
    box-sizing: border-box; 
    font-family: coolvetica, Helvetica, sans-serif;
}

:root{
    --hue-neutral: 200;
    --hue-wrong: 0;
    --hue-correct: 145;
}

body{
    --hue: var(--hue-neutral);
    padding: 0;
    margin: 0;
    display: flex;
    width: 100vw;
    height: 100vh;
    justify-content: center;
    align-items: center;
    background-color: hsl(var(--hue), 100%, 20%);
}

body.correct {
    --hue: var(--hue-correct);
} 

body.wrong {
    --hue: var(--hue-wrong);
}

.container {
    width: 800px;
    max-width: 80%;
    background-color: #fff;
    border-radius: 5px;
    padding: 10px;
    box-shadow: 0 0 10px 2px;
}

.btn-grid{
    display: grid;
    grid-template-columns: repeat(2,auto);
    gap: 10px;
    margin: 20px 0;
}

.btn {
    --hue: var(--hue-neutral);
    border: 1px solid hsl(var(--hue), 100%, 30%);
    background-color: hsl(var(--hue), 100%, 50%);
    border-radius: 5px;
    padding: 5px 10px;
    color: #fff;
    outline: none;
    font-size: 16px;
}

.btn:hover {
    border-color: black;

} 

.btn.correct{
--hue: var(--hue-correct);
color: black;

}

.btn.wrong{
--hue: var(--hue-wrong);
}

.start-btn, .next-btn{
    font-size: 1.5rem;
    font-weight: bold;
    padding: 10px;
    margin: 20px;
    background-color: hsl(var(--hue), 100%, 50%);
    color: #fff;

}

.controls{
    display:flex;
    justify-content: center;
    align-items: center;
}

.hide{
    display: none;
}