css.css

html {
  box-sizing: border-box;
}
*, *:before, *:after {
  box-sizing: inherit;
}
html, body {
  margin: 0;
  height: 100%;
}
#c {
  width: 100%;
  height: 100%;
  display: block;
}
#loading {
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  font-size: xx-large;
  font-family: sans-serif;
}
#loading>div>div {
  padding: 2px;
}
.progress {
  width: 50vw;
  border: 1px solid black;
}
#progressbar {
  width: 0%;
  transition: width ease-out .5s;
  height: 1em;
  background-color: #888;
  background-image: linear-gradient(
  -45deg,
  rgba(255, 255, 255, .5) 25%,
  transparent 25%,
  transparent 50%,
  rgba(255, 255, 255, .5) 50%,
  rgba(255, 255, 255, .5) 75%,
  transparent 75%,
  transparent
  );
  background-size: 50px 50px;
  animation: progressanim 2s linear infinite;
}

@keyframes progressanim {
  0% {
    background-position: 50px 50px;
  }
  100% {
    background-position: 0 0;
  }
}