style.css

* {
    text-align: center;
    position: relative;
    margin: auto;
    background-color: black;
    color: white;
}

body {
    display: block;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    animation: startFade 1s;
}

.btn {
    transition: 0.5s all ease-out;
    font-size: 125%;
    border-radius: 5px;
    border: 5px;
    outline: solid;
    outline-width: 3px;
    outline-color: white;
    width: 150px;
    height: 40px;
}

.btn:hover {
    outline-color: greenyellow;
    scale: 1.1;
    cursor: pointer;
}

.btn:active {
    transition: 0.1s all linear;
    filter: brightness(70%);
    scale: 1;
}

.typeWriter {
    overflow: hidden;
    border-right: 1.5em solid yellowgreen;
    border-right-width: 0.1em;
    white-space: nowrap;
    animation: typing 1s steps(20, end) forwards, blinking .8s infinite;
    font-size: 1.6rem;
    width: 0;
}

.container {
    display: inline-block;
}

@keyframes startFade {
    0% {
        opacity: 0;
    }

    100% {
        opacity: 1;
    }
}

@keyframes typing {
    from {
        width: 0;
    }

    to {
        width: 100%;
    }
}

@keyframes blinking {
    from {
        border-color: transparent;
    }

    to {
        border-color: greenyellow;
    }
}