Fix 'basic:export-scss' test

Author: Semigradsky

plugins/postcss-custom-properties/test/export-properties.scss

@@ -7,4 +7,7 @@ $color-hsl: hsl(var(--color-h), var(--color-s), var(--color-l));
 $circular: var(--circular-2);
 $circular-2: var(--circular);
 $margin: 0 10px 20px 30px;
+$shadow-color: rgb(255,0,0);
+$shadow: 0 6px 14px 0 color(var(--shadow-color) a(.15));
+$font-family: "Open Sans" , sans-serif;
 $theme-color: #053;