refactor(progressbar): add comments to clarify why we use px for --stroke-thickness

Author: desig9stein

src/components/progress/themes/circular/shared/circular.progress.bootstrap.scss

@@ -4,6 +4,9 @@
 $theme: $bootstrap;
 
 :host {
+    // Do not use rem values here
+    // This will break the component in Safari
+    // https://github.com/IgniteUI/igniteui-webcomponents/issues/377
     --stroke-thickness: 2px;
     --scale-factor: 3.05;
 }

src/components/progress/themes/circular/shared/circular.progress.fluent.scss

@@ -6,6 +6,9 @@
 $theme: $fluent;
 
 :host {
+    // Do not use rem values here
+    // This will break the component in Safari
+    // https://github.com/IgniteUI/igniteui-webcomponents/issues/377
     --stroke-thickness: 2px;
     --scale-factor: 2.75;
 }

src/components/progress/themes/circular/shared/circular.progress.indigo.scss

@@ -4,7 +4,10 @@
 $theme: $indigo;
 
 :host {
-    --stroke-thickness: rem(3px);
+    // Do not use rem values here
+    // This will break the component in Safari
+    // https://github.com/IgniteUI/igniteui-webcomponents/issues/377
+    --stroke-thickness: 3px;
     --scale-factor: 3.4;
 }