<div class="element"></div>

body {
  background-image: radial-gradient( circle 360px at 50% 50%,  rgba(54,96,172,1) 0%, rgba(46,53,89,1) 100.2% );
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  margin: 0;
}

.element {
  width: 0;
  height: 0;
  border: 50px solid transparent;
  border-bottom-color: #fff;
  border-left-color: #fff;
}