Initial version

themes/zen/assets/sass/base/document/_document.scss

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+// Document
+
+html {
+  // Change the default font family in all browsers.
+  font-family: var(--ff-body);
+  // Set base font size in percent.
+  font-size: calc(#{$base-font-size} / 16 * 100%);
+  // Correct the line height in all browsers.
+  line-height: $base-line-height;
+  // Set text colour.
+  color: var(--color-text);
+}
+
+body {
+  // Output a horizontal grid to help with debugging typography. The
+  // $debug variable will toggle its output.
+  @include debug-grid();
+}