style.css

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

html {
    font-size: 62.5%;
}

body {
    font-family: 'Roboto', Arial, Helvetica, sans-serif;
    color: #ffffff;
    background-color: #000000;
}

.title h2 {
    text-align: center;
    font-size: 4rem;
}

.title p {
    font-size: 2.5rem;
}

.results p {
    font-size: 2rem;
}

.container {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
}

.animation {
    animation: shake 0.82s cubic-bezier(.36, .07, .19, .97) both;
    transform: translate3d(0, 0, 0);
    backface-visibility: hidden;
    perspective: 1000px;
}

@keyframes shake {
    10%, 90% {
        transform: translate3d(-1px, 0, 0);
    }
    20%, 80% {
        transform: translate3d(2px, 0, 0);
    }
    30%, 50%, 70% {
        transform: translate3d(-4px, 0, 0);
    }
    40%, 60% {
        transform: translate3d(4px, 0, 0);
    }
}

.contents {
    padding: 40px;
    background-color: black;
    width: 90vw;
    margin: 15px;
    border-radius: 15px;
}

.subtitle {
    margin-top: 10px;
    display: none;
}

input[type="number"] {
    width: 100%;
    padding: 2rem;
    transition: 0.5s;
    border: 2px solid #000000;
}

input[type="number"]::placeholder {
    font-size: 2rem;
}

input[type="number"]:focus {
    outline: none;
    border: 2px solid purple;
}

input[type=number]::-webkit-inner-spin-button, input[type=number]::-webkit-outer-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

.inputs {
    display: flex;
    margin-top: 40px;
}

.playBtn, .playAgainBtn {
    width: 50%;
    text-transform: uppercase;
    padding: 10px 10px;
    background-color: purple;
    border-radius: 5px;
    margin-left: 5px;
    font-size: 2rem;
    font-weight: 700;
    color: white;
    outline-color: transparent;
    cursor: pointer;
    border: none;
    box-shadow: 0 5px 3px rgba(0, 0, 0, 0.3);
}

.playBtn:hover {
    transition: background-color 0.5s ease-in-out;
    background-color:purple;
}

.playAgainBtn {
    margin-top: 15px;
    width: 100%;
}

.playAgainBtn:hover {
    transition: background-color 0.5s ease-in-out;
    background-color: purple;
}

.attempt, .result {
    margin-top: 35px;
}

@media screen and (max-width: 570px) {
    input[type="number"]::-webkit-input-placeholder {
        color: transparent;
    }
}

@media screen and (min-width: 768px) {
    input[type='number'] {
        width: 70%;
    }
    .inputs {
        margin: 40px auto;
    }
    .playAgainBtn {
        width: 50%;
    }
}