feat(combobox-item): update idle icons (#11801)

**Related Issue:** #10580

## Summary
Updated selection icons in the idle state.

Author: josercarcamo

packages/calcite-components/src/components/combobox-item/combobox-item.scss

@@ -112,13 +112,13 @@ ul:focus {
 
 .icon {
   @apply inline-flex
-    opacity-0
     duration-150
     ease-in-out;
+
+  color: var(--calcite-color-border-input);
 }
 
 :host([selected]) .icon {
-  @apply opacity-100;
   color: var(--calcite-combobox-selected-icon-color, var(--calcite-color-brand));
 }
 

packages/calcite-components/src/components/combobox-item/combobox-item.tsx

@@ -280,7 +280,13 @@ export class ComboboxItem extends LitElement implements InteractiveComponent {
     } = this;
     const isSingleSelect = isSingleLike(this.selectionMode);
     const icon = disabled || isSingleSelect ? undefined : "check-square-f";
-    const selectionIcon = isSingleSelect ? "circle-inset-large" : "check-square-f";
+    const selectionIcon = isSingleSelect
+      ? this.selected
+        ? "circle-inset-large"
+        : "circle"
+      : this.selected
+        ? "check-square-f"
+        : "square";
     const headingText = heading || textLabel;
     const itemLabel = label || value;