Address maintainer review feedback

Consolidate styles in style sheet in favor of utility classes.

app/assets/javascripts/batch_comments/components/review_bar.vue

@@ -26,10 +26,7 @@ export default {
 </script>
 <template>
   <div v-show="draftsCount > 0">
-    <nav
-      class="review-bar-component gl-bg-white gl-w-full gl-fixed gl-left-0 gl-bottom-0 gl-display-flex gl-align-items-center"
-      data-testid="review_bar_component"
-    >
+    <nav class="review-bar-component" data-testid="review_bar_component">
       <div
         class="review-bar-content d-flex gl-justify-content-end"
         data-qa-selector="review_bar_content"

app/assets/stylesheets/components/batch_comments/review_bar.scss

 .review-bar-component {
+  position: fixed;
+  bottom: 0;
+  left: 0;
   z-index: $zindex-dropdown-menu;
-  border-top: 1px solid $border-color;
+  display: flex;
+  align-items: center;
+  width: 100%;
   height: $toggle-sidebar-height;
   padding-left: $contextual-sidebar-width;
   padding-right: $gutter_collapsed_width;
+  background: $white;
+  border-top: 1px solid $border-color;
   transition: padding $sidebar-transition-duration;
 
   .page-with-icon-sidebar & {