Generated by SassMeister.com.

SassMeister-input-HTML.html

<main>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
</main>

SassMeister-input.scss

// ----
// Sass (v3.4.14)
// Compass (v1.0.3)
// ----

main {
  background: lightblue;
  display: flex;
  margin: 0 auto;
  overflow: hidden;
  flex-flow: row wrap;
  width: 800px;
}

div {
  background: darkgreen;
  flex: {
    basis: calc(25% - 2rem);
    grow: 1;
    shrink: 0;
  };
  height: 100px;
  margin: 1rem;
}

SassMeister-output.css

main {
  background: lightblue;
  display: flex;
  margin: 0 auto;
  overflow: hidden;
  flex-flow: row wrap;
  width: 800px;
}

div {
  background: darkgreen;
  flex-basis: calc(25% - 2rem);
  flex-grow: 1;
  flex-shrink: 0;
  height: 100px;
  margin: 1rem;
}

SassMeister-rendered.html

<main>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
</main>