.background {
    position: fixed;
    width: 100%;
    height: 100vh;
    z-index: -1;
}

.letter1, .letter2 {
    position: absolute;
    font-size: 2em;
    color: #4d5056;
}

.letter1 {
    animation: move1 10s linear infinite;
}

.letter2 {
    animation: move2 10s linear infinite;
}

@keyframes move1 {
    from {
        left: -100px;
    }
    to {
        left: calc(50% + 500px);
    }
}

@keyframes move2 {
    from {
        left: calc(50% + 500px);
    }
    to {
        left: calc(100% + 1100px);
    }
}