replace deprecated slash division with math division in Sass

Change-Id: I664c367e06eb166f74197ac50ef90dc24a7b5ef9
diff --git a/dev/scss/sidebar/sidebar.scss b/dev/scss/sidebar/sidebar.scss
index 01979b4..da6541f 100644
--- a/dev/scss/sidebar/sidebar.scss
+++ b/dev/scss/sidebar/sidebar.scss
@@ -1,4 +1,5 @@
 @charset "utf-8";
+@use 'sass:math';
 @import "../util";
 
 aside {
@@ -41,7 +42,7 @@
     padding:   6pt;
     background-color: $dark-green;
     border-top-right-radius: $standard-border-radius;
-    margin-right: -1 * ($standard-margin / 2);
+    margin-right: -1 * math.div($standard-margin,2);
   }
 
   &.settings::after {
@@ -203,7 +204,7 @@
   // Off aside
   &.off,
   &:not(:focus):not(.active) {
-    margin-left: -1 * ($logo-left-distance - ($standard-margin / 2));
+    margin-left: -1 * ($logo-left-distance - math.div($standard-margin,2));
     &::after {
       opacity: 1;
     }