styles.css

/*noinspection CssUnknownTarget*/
@import url('https://fonts.googleapis.com/css2?family=Press+Start+2P&display=swap');

* {
    margin: 0;
    padding: 0;
    box-sizing: content-box;
}

:root {
    --textColor: hsl(240, 2%, 91%);
    --backgroundColor: hsl(0, 0%, 12%);
    font-family: 'Press Start 2P', cursive;
    color: var(--textColor);
    background-color: var(--backgroundColor);
}

h1 {
    text-align: center;
    font-size: 2.5rem;
}

main {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-content: center;
}

.header {
    margin: 2rem 1rem;
    padding: 1rem;
    display: flex;
    justify-content: space-between;
    text-align: center;
}


.number {
    margin: 2rem 0;
    height: 6rem;
    width: 100%;
    display: flex;
    justify-content: center;
}

.number > h1 {
    background-color: var(--textColor);
    width: 8rem;
    color: var(--backgroundColor);
    vertical-align: middle;
    text-align: center;
    line-height: 6rem;
    font-size: 2.5rem;
}

.line {
    width: 100%;
    height: 7px;
    background-color: var(--textColor);
    position: absolute;
    transform: translateY(3rem);
    z-index: -1;
}

.btn {
    font-family: 'Press Start 2P', cursive;
    padding: 1rem 1.5rem;
    border: 0;
    box-shadow: none;
    border-radius: 1px;
    font-size: 1.1rem;
}

.interactive {
    margin: 2rem;
    padding: 1rem 9rem;
    display: flex;
    justify-content: space-evenly;
}

.guess {
    display: inline-flex;
    flex-direction: column;
    justify-content: center;
    align-content: center;
    width: auto;
}

/* submit button */
.guess > button {
    margin: 3rem auto;

}

.guess > input {
    margin: 1px auto;
    border: solid 3px var(--textColor);
    border-radius: 0;

    background-color: var(--backgroundColor);
    color: var(--textColor);
    padding: 2rem 1rem;
    font-size: 2rem;
    width: 50%;

    font-family: inherit;
    text-align: center;
}


.analytics {
    font-size: 1.3rem;
}

.analytics > * {
    margin: 1rem;
}

.analytics > :first-child {
    margin-top: 0;
    margin-bottom: 5rem;
}

@media only screen and (max-width: 768px) {
    /* For mobile phones: */
    /*body {*/
    /*    background-color: aqua;*/
    /*}*/
    :root {
        font-size: 13px;
    }

    .btn {
        padding: .5rem .75rem;
        font-size: 1rem;
    }

    .header {
        align-content: center;
    }

    .header > p {
        font-size: .7rem;
    }

    .interactive {
        padding: inherit;
    }

    .analytics {
        font-size: 1.1rem;
    }

    .guess > input {
        font-size: 1.5rem;
    }

    .analytics > :not(:first-child) {
        font-size: .8rem;
    }
}