<div class="marquee">
    <ul class="marquee-content">
      <li><i class="fab fa-github"></i></li>
      <li><i class="fab fa-codepen"></i></li>
      <li><i class="fab fa-free-code-camp"></i></li>
      <li><i class="fab fa-dev"></i></li>
      <li><i class="fab fa-react"></i></li>
      <li><i class="fab fa-vuejs"></i></li>
      <li><i class="fab fa-angular"></i></li>
      <li><i class="fab fa-node"></i></li>
      <li><i class="fab fa-wordpress"></i></li>
      <li><i class="fab fa-aws"></i></li>
      <li><i class="fab fa-docker"></i></li>
      <li><i class="fab fa-android"></i></li>
    </ul>
  </div>

@import url('https://fonts.googleapis.com/css?family=Montserrat');

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  font-family: 'Montserrat', sans-serif;
  background-color: #eee;
  color: #111;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

:root {
  --marquee-width: 80vw;
  --marquee-height: 20vh;
  /* --marquee-elements: 12; */ /* defined with JavaScript */
  --marquee-elements-displayed: 5;
  --marquee-element-width: calc(var(--marquee-width) / var(--marquee-elements-displayed));
  --marquee-animation-duration: calc(var(--marquee-elements) * 3s);
}

.marquee {
  width: var(--marquee-width);
  height: var(--marquee-height);
  background-color: #111;
  color: #eee;
  overflow: hidden;
  position: relative;
}
.marquee:before, .marquee:after {
  position: absolute;
  top: 0;
  width: 10rem;
  height: 100%;
  content: "";
  z-index: 1;
}
.marquee:before {
  left: 0;
  background: linear-gradient(to right, #111 0%, transparent 100%);
}
.marquee:after {
  right: 0;
  background: linear-gradient(to left, #111 0%, transparent 100%);
}
.marquee-content {
  list-style: none;
  height: 100%;
  display: flex;
  animation: scrolling var(--marquee-animation-duration) linear infinite;
}
/* .marquee-content:hover {
  animation-play-state: paused;
} */
@keyframes scrolling {
  0% { transform: translateX(0); }
  100% { transform: translateX(calc(-1 * var(--marquee-element-width) * var(--marquee-elements))); }
}
.marquee-content li {
  display: flex;
  justify-content: center;
  align-items: center;
  /* text-align: center; */
  flex-shrink: 0;
  width: var(--marquee-element-width);
  max-height: 100%;
  font-size: calc(var(--marquee-height)*3/4); /* 5rem; */
  white-space: nowrap;
}

.marquee-content li img {
  width: 100%;
  /* height: 100%; */
  border: 2px solid #eee;
}

@media (max-width: 600px) {
  html { font-size: 12px; }
  :root {
    --marquee-width: 100vw;
    --marquee-height: 16vh;
    --marquee-elements-displayed: 3;
  }
  .marquee:before, .marquee:after { width: 5rem; }
}

const root = document.documentElement;
const marqueeElementsDisplayed = getComputedStyle(root).getPropertyValue("--marquee-elements-displayed");
const marqueeContent = document.querySelector("ul.marquee-content");

root.style.setProperty("--marquee-elements", marqueeContent.children.length);

for(let i=0; i<marqueeElementsDisplayed; i++) {
  marqueeContent.appendChild(marqueeContent.children[i].cloneNode(true));
}