replace deprecated slash division with math division in Sass

Change-Id: I664c367e06eb166f74197ac50ef90dc24a7b5ef9
diff --git a/dev/scss/footer/footer.scss b/dev/scss/footer/footer.scss
index 76f2846..97cfce8 100644
--- a/dev/scss/footer/footer.scss
+++ b/dev/scss/footer/footer.scss
@@ -1,4 +1,5 @@
 @charset "utf-8";
+@use 'sass:math';
 @import "../util";
 
 /**
@@ -73,12 +74,12 @@
  */
 #ids-logo {
   display:          inline-block;
-  width:            (631 / 30) + em;
-  height:           (200 / 30) + em;
+  width:            math.div(631,30) + em;
+  height:           math.div(200,30) + em;
   background-image: url('#{$img-path}/ids-institute-for-the-german-language-white.svg');
 }
 
 aside.active ~ footer {
   padding-left: $logo-left-distance;
   transition:  all .3s ease-in-out;
-}
\ No newline at end of file
+}