update gemfile following bundler update and fix deprecation warning

Gemfile.lock

 GEM
   remote: https://rubygems.org/
   specs:
-    addressable (2.7.0)
-      public_suffix (>= 2.0.2, < 5.0)
+    addressable (2.8.4)
+      public_suffix (>= 2.0.2, < 6.0)
     colorator (1.1.0)
-    concurrent-ruby (1.1.8)
-    em-websocket (0.5.2)
+    concurrent-ruby (1.2.2)
+    em-websocket (0.5.3)
       eventmachine (>= 0.12.9)
-      http_parser.rb (~> 0.6.0)
+      http_parser.rb (~> 0)
     eventmachine (1.2.7)
-    ffi (1.14.2)
+    ffi (1.15.5)
     forwardable-extended (2.6.0)
-    http_parser.rb (0.6.0)
-    i18n (1.8.9)
+    google-protobuf (3.23.3-x86_64-linux)
+    http_parser.rb (0.8.0)
+    i18n (1.14.1)
       concurrent-ruby (~> 1.0)
-    jekyll (4.2.0)
+    jekyll (4.3.2)
       addressable (~> 2.4)
       colorator (~> 1.0)
       em-websocket (~> 0.5)
       i18n (~> 1.0)
-      jekyll-sass-converter (~> 2.0)
+      jekyll-sass-converter (>= 2.0, < 4.0)
       jekyll-watch (~> 2.0)
-      kramdown (~> 2.3)
+      kramdown (~> 2.3, >= 2.3.1)
       kramdown-parser-gfm (~> 1.0)
       liquid (~> 4.0)
-      mercenary (~> 0.4.0)
+      mercenary (>= 0.3.6, < 0.5)
       pathutil (~> 0.9)
-      rouge (~> 3.0)
+      rouge (>= 3.0, < 5.0)
       safe_yaml (~> 1.0)
-      terminal-table (~> 2.0)
-    jekyll-sass-converter (2.1.0)
-      sassc (> 2.0.1, < 3.0)
+      terminal-table (>= 1.8, < 4.0)
+      webrick (~> 1.7)
+    jekyll-sass-converter (3.0.0)
+      sass-embedded (~> 1.54)
     jekyll-watch (2.2.1)
       listen (~> 3.0)
-    kramdown (2.3.0)
+    kramdown (2.4.0)
       rexml
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
-    liquid (4.0.3)
-    listen (3.4.1)
+    liquid (4.0.4)
+    listen (3.8.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
     mercenary (0.4.0)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
-    public_suffix (4.0.6)
-    rb-fsevent (0.10.4)
+    public_suffix (5.0.1)
+    rake (13.0.6)
+    rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.2.4)
-    rouge (3.26.0)
+    rexml (3.2.5)
+    rouge (4.1.2)
     safe_yaml (1.0.5)
-    sassc (2.4.0)
-      ffi (~> 1.9)
-    terminal-table (2.0.0)
-      unicode-display_width (~> 1.1, >= 1.1.1)
-    unicode-display_width (1.7.0)
+    sass-embedded (1.63.6)
+      google-protobuf (~> 3.23)
+      rake (>= 13.0.0)
+    terminal-table (3.0.2)
+      unicode-display_width (>= 1.1.1, < 3)
+    unicode-display_width (2.4.2)
+    webrick (1.8.1)
 
 PLATFORMS
-  ruby
+  x86_64-linux
 
 DEPENDENCIES
   jekyll
 
 BUNDLED WITH
-   2.1.4
+   2.4.15

_sass/variables.scss

@@ -10,7 +10,7 @@ $resp-small-font-size: 12px;
 $resp-big-font-size: 16px;
 
 $padding-std: 8px;
-$padding-small: $padding-std / 2.1;
+$padding-small: calc($padding-std / 2.1);
 $padding-big: 3 * $padding-std;
 $line-height-std: 1.4;
 $border-std: 1px;
@@ -22,8 +22,8 @@ $resp-margin-std: 80px;
 $resp-margin-small: $resp-margin-std * 0.7;
 $resp-margin-big: 2 * $resp-margin-std;
 
-$box-size: $max-width / 3 - $margin-std;
-$resp-box-size: $resp-max-width / 3 - $resp-margin-std;
+$box-size: calc($max-width / 3) - $margin-std;
+$resp-box-size: calc($resp-max-width / 3) - $resp-margin-std;
 
 $color-strong: hsl(221, 81%, 30%);
 $color-fade: hsl(221, 81%, 95%);