style.css

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

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

html {
    font-size: 52%;
    box-sizing: border-box;
}

body {
    font-family: 'Press Start 2P', sans-serif;
    color: #eee;
    background-color: #222;
}

/* LAYOUT */
header {
    position: relative;
    height: 50vh;
    border-bottom: 7px solid #eee;
}

main {
    height: 50vh;
    color: #eee;
    display: flex;
    align-items: center;
    justify-content: space-around;
}

.left {
    width: 52rem;
    display: flex;
    flex-direction: column;
    align-items: center;
}

.right {
    width: 52rem;
    font-size: 2rem;
}

/* ELEMENTS STYLE */
h1 {
    font-family: 'Nabla', sans-serif;
    font-size: 6rem;
    text-align: center;
    position: absolute;
    width: 100%;
    top: 52%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.number {
    background: #eee;
    color: #333;
    font-size: 6rem;
    width: 15rem;
    padding: 3.5rem 0 3rem 1rem;
    text-align: center;
    position: absolute;
    bottom: 0;
    left: 50%;
    transform: translate(-50%, 50%);
}

.between {
    font-size: 1.4rem;
    position: absolute;
    top: 2rem;
    right: 2rem;
    width: 50%;
    line-height: 2rem;
    text-align: end;
}

.between > span {
    color: #fdc322;
}

.again {
    position: absolute;
    top: 2rem;
    left: 2rem;
}

.guess {
    background: none;
    border: 4px solid #eee;
    font-family: inherit;
    color: inherit;
    font-size: 5rem;
    width: 25rem;
    text-align: center;
    display: block;
    margin-bottom: 3rem;
    padding: 2.5rem 0 2.5rem 2.5rem;
}

.btn {
    border: none;
    background-color: #eee;
    color: #222;
    font-size: 2rem;
    font-family: inherit;
    padding: 2.3rem 2rem 2rem 3rem;
    cursor: pointer;
}

.btn:hover:enabled {
    background-color: #fdc322;
}

button:disabled {
    border: 1px solid #fdc322;
    background-color: #0c4502;
    color: #eeeeee;
}

.message {
    margin-bottom: 8rem;
    height: 3rem;
}

.label-score {
    margin-bottom: 2rem;
}

.label-highscore {
    color: #fdc322;
}