body {
    background-color: khaki;
    padding: 0.5rem 1rem;
}

h1 {
    text-align: center;
}

.container {
    text-align: center;
}

#timer {
    font-size: 3rem;
}

.buttons {
    display: flex;
    justify-content: center;
    gap: 1rem;
}

.operate-button {
    font-size: 1.5rem;
    padding: 0.25rem 0.5rem;
    background-color: skyblue;
    border-radius: 0.5rem;
}

#result {
    margin: 2rem auto;
    width: 16rem;
    font-size: 1.25rem;
    background-color: darkkhaki;
    border-radius: 1rem;
    color: white;
    padding: 1rem 1rem;
}

#diff,
#grade {
    font-size: 2rem;
    font-weight: bold;
    font-family: numberonly, monospace, sans-serif;
}

#history {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    justify-content: center;
    max-width: 30rem;
    margin: 0 auto;
    gap: 0.75rem;
}

#history>div {
    font-weight: bold;
    background-color: darkkhaki;
    padding: 0.25rem 0.5rem;
    border-radius: 1rem;
}