why left 50% fixed element not centere code example

Example 1: center position fixed

.centered {
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

Example 2: how to middle fixed element

position: fixed;
	top: 0;
	z-index: 100;
	left: 50%;
	transform: translateX(-50%);