<div class="loader"></div>
.loader {
  --s: 100px; /* control the size */
  
  --_d: calc(0.353*var(--s));/* 0.353 = sin(45deg)/2 */
  height: var(--s); 
  aspect-ratio: 3;
  display: flex;
}
.loader:before,
.loader:after {
  content: "";
  clip-path: polygon(var(--_d) 0,100% 0,100% calc(100% - var(--_d)),calc(100% - var(--_d)) 100%,0 100%,0 var(--_d));
  background:
    conic-gradient(from -90deg at calc(100% - var(--_d)) var(--_d),
     #fff 135deg,#666 0 270deg,#aaa 0);
}
.loader:before {  
  background-color: #CC333F; /* control the color here */
  background-blend-mode: multiply;
  margin-right: calc(var(--_d)/-2);
  animation: load 2.5s infinite linear;
}
.loader:after {
  margin-left: calc(var(--_d)/-2);
  opacity: 0.4;
  flex: 1;
}

@keyframes  load {
  0%,
  5%   {width: 0%}
  95%,
  100% {width: 100%}
}


body {
  margin: 0;
  height: 100vh;
  display: grid;
  place-content: center;
  background: #000;
}

External CSS

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External JavaScript

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