<div class="columns">
  <div class="col col-2 col-bg-aqua">
    <h2>Section 1 - Col 1</h2>
    <p>This is column 1</p>
  </div>
  <div class="col col-1 col-bg-beige">
    <h2>Section 1 - Col 2</h2>
    <p>This is column 2</p>
  </div>
  <div class="col col-1">
    <h2>Section 1 - Col 3</h2>
    <p>This is column 3</p>
  </div>
</div>

.container {
  width: 90%;
  max-width: 980px;
  margin: 0 auto;
}
.columns {
  display: flex;
  margin: 1em 0;
}
.col-bg-beige {
  background-color: beige;
  padding: 1em;
}
.col-bg-aqua {
  background-color: aqua;
  padding: 1em;
}

.col-1 {
  width: 25%;
}
.col-2 {
  width: 50%;
}
.col-3 {
  width: 75%;
}
.col-4 {
  width: 100%;
}