Reduce motion for boost animation (#5871)

* Reduce motion for boost animation

Fixes #5833

* Fix ternary expression

app/javascript/styles/mastodon/components.scss

@@ -2149,7 +2149,8 @@
 
 @import 'boost';
 
-button.icon-button i.fa-retweet {
+.no-reduce-motion button.icon-button i.fa-retweet {
+
   background-position: 0 0;
   height: 19px;
   transition: background-position 0.9s steps(10);
@@ -2160,13 +2161,23 @@ button.icon-button i.fa-retweet {
   &::before {
     display: none !important;
   }
+
 }
 
-button.icon-button.active i.fa-retweet {
+.no-reduce-motion button.icon-button.active i.fa-retweet {
   transition-duration: 0.9s;
   background-position: 0 100%;
 }
 
+.reduce-motion button.icon-button i.fa-retweet {
+  color: $ui-base-lighter-color;
+  transition: color 100ms ease-in;
+}
+
+.reduce-motion button.icon-button.active i.fa-retweet {
+  color: $ui-highlight-color;
+}
+
 .status-card {
   display: flex;
   cursor: pointer;

app/views/layouts/application.html.haml

@@ -28,6 +28,7 @@
 
   - body_classes ||= @body_classes || ''
   - body_classes += ' system-font' if current_account&.user&.setting_system_font_ui
+  - body_classes += current_account&.user&.setting_reduce_motion ? ' reduce-motion' : ' no-reduce-motion'
 
   %body{ class: add_rtl_body_class(body_classes) }
     = content_for?(:content) ? yield(:content) : yield