<div class="wrapper">
    <div class="child"></div>
</div>

.wrapper {
  height: 200px;
  max-width: 400px;
  margin-right: auto;
  margin-left: auto;
  background-color: lightblue;
}

.child {
  width: 100vw;
  height: 100px;
  margin-left: calc((100% - 100vw) / 2);
  background-color: lightgreen;
}




* {
  box-sizing: border-box;
}

body {
  margin: 0;
  overflow-x: hidden;
}