How to Make Full-Width Items in a Container with Padding in CSS?

<div class="container">
  <div class="item">Section 1</div>
  <div class="item">Section 2</div>
  <div class="item">Section 3</div>
  <div class="item">Section 4</div>
  <div class="item">Section 5</div>
</div>

html, body {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
}

.container {
  background-color: red;
  width: 100%;
  height: 100%;
  padding: 0 20px;
}

.item {
  width: 100%;
  height: 20%;
}

.item:nth-child(odd) {
  background-color: blue;
}

.item:nth-child(even) {
  background-color: green;
}