style.css

html {
    height: 100%;
}

body {
    font-family: 'Source Sans Pro', sans-serif;
    background: #131313;
    color: white;
    display: flex;
    justify-content: center;
    align-items: center;
    margin: 0;
    padding: 0;
}

.top-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 20px;
    margin: 20px;
}

.top-nav a {
    display: flex;
    text-decoration: none;
    color: #fff;
    text-shadow: 2px 2px #00aeff;
}

.top-nav h1 {
    font-size: 50px;
    margin: 0;
    width: 240px;
}

a {
    text-decoration: none;
    color: #fff;
    text-shadow: 2px 2px #00aeff;
}

a i {
    margin: 5px 15px;
}

h2 {
    text-shadow: 2px 2px #00aeff;
    margin: 0 20px;
    font-size: 32px;
}

.wrapper {
    text-align: center;
    width: 500px;
    margin: 0 20px;
}

.boxes {
    display: flex;
    justify-content: center;
    font-size: 60px;
    color: #fff;
    background: rgba(255, 255, 255, 0.05);
    border-radius: 16px;
    margin: 20px auto;
    padding: 9px;
}

#box {
    width: 60px;
    height: 60px;
    border: 3px solid #fff;
    border-radius: 10px;
    margin: 0 5px;
    text-shadow: 2px 2px #00aeff;
    box-shadow: 2px 2px #00aeff;
    display: flex;
    align-items: center;
    justify-content: center;
}

.keyboard {
    display: flex;
    flex-direction: column;
    align-items: center;
    width: 100%;
    max-width: 500px;
    margin: 0 auto;
}

.row {
    display: flex;
    margin: 5px 0;
    margin-top: 0;
    justify-content: space-between;
    width: 100%;
}

.keyboard-button {
    flex-grow: 1;
    min-width: 5%;
    height: 55px;
    font-size: 16px;
    font-weight: bold;
    border: 1px solid #fff;
    border-radius: 3px;
    margin: 0 3px;
    cursor: pointer;
    text-shadow: 2px 2px #00aeff;
    box-shadow: 2px 2px #00aeff;
}

.delete {
    background-color: rgb(255, 100, 100);
    min-width: 15%;
}

.enter {
    background-color: rgb(75, 190, 75);
    min-width: 20%;
}

@media (max-width: 500px) {
    .top-nav h1 {
        font-size: 46px;
        width: 220px;
    }
    h2 {
        font-size: 28px;
    }
}

@media (max-width: 400px) {
    .top-nav h1 {
        font-size: 42px;
        width: 200px;
    }
    h2 {
        font-size: 24px;
    }
}

@media (max-width: 375px) {
    .top-nav h1 {
        font-size: 40px;
        width: 190px;
    }
    h2 {
        font-size: 22px;
    }
    .keyboard-button {
        font-size: 16px;
    }
}