Operators

Sass has a handful of standard math operators
like +, -, *, math.div()

@use "sass:math";

.container {
  display: flex;
}

article[role="main"] {
  width: math.div(600px, 960px) * 100%;
}

aside[role="complementary"] {
  width: math.div(300px, 960px) * 100%;
  margin-left: auto;
}

.container {
  display: flex;
}

article[role=main] {
  width: 62.5%;
}

aside[role=complementary] {
  width: 31.25%;
  margin-left: auto;
}