Use `IconButton`, `LabeledButton` in `Thread`

Replace uses of `Button` in the Thread component and adjust
styling for stronger alignment in both desktop and touch interfaces.

src/sidebar/components/Thread.js

@@ -5,8 +5,9 @@ import { useStoreProxy } from '../store/use-store';
 import { withServices } from '../service-context';
 import { countHidden, countVisible } from '../helpers/thread';
 
+import { IconButton, LabeledButton } from '../../shared/components/buttons';
+
 import Annotation from './Annotation';
-import Button from './Button';
 import ModerationBanner from './ModerationBanner';
 
 /** @typedef {import('../helpers/build-thread').Thread} Thread */
@@ -90,24 +91,29 @@ function Thread({ thread, threadsService }) {
     >
       {showThreadToggle && (
         <div className="Thread__collapse">
-          <Button
-            className="Thread__collapse-button"
+          <div className="Thread__collapse-button-container">
+            <IconButton
+              className="NonResponsiveIconButton"
+              expanded={!thread.collapsed}
               icon={toggleIcon}
               title={toggleTitle}
               onClick={onToggleReplies}
+              size="medium"
+              variant="light"
             />
           </div>
+        </div>
       )}
 
       <div className="Thread__content">
         {annotationContent}
 
         {showHiddenToggle && (
-          <Button
-            buttonText={`Show ${countHidden(thread)} more in conversation`}
-            className="Thread__hidden-toggle-button"
-            onClick={() => threadsService.forceVisible(thread)}
-          />
+          <div className="Thread__hidden-toggle-button-container">
+            <LabeledButton onClick={() => threadsService.forceVisible(thread)}>
+              Show {countHidden(thread)} more in conversation
+            </LabeledButton>
+          </div>
         )}
 
         {showChildren && (

src/sidebar/components/test/Thread-test.js

@@ -111,7 +111,7 @@ describe('Thread', () => {
 
     // Retrieve the (caret) button for showing and hiding replies
     const getToggleButton = wrapper => {
-      return wrapper.find('Button').filter('.Thread__collapse-button');
+      return wrapper.find('IconButton');
     };
 
     beforeEach(() => {
@@ -178,7 +178,9 @@ describe('Thread', () => {
       collapsedThread.parent = '1';
       const wrapper = createComponent({ thread: collapsedThread });
 
-      assert.isTrue(wrapper.find('.Thread__collapse-button').exists());
+      assert.isTrue(
+        wrapper.find('IconButton[title="Expand replies"]').exists()
+      );
     });
 
     it('does not render child threads', () => {
@@ -231,11 +233,7 @@ describe('Thread', () => {
       const wrapper = createComponent({ thread });
 
       act(() => {
-        wrapper
-          .find('Button')
-          .filter({ buttonText: 'Show 1 more in conversation' })
-          .props()
-          .onClick();
+        wrapper.find('LabeledButton').props().onClick();
       });
 
       assert.calledOnce(fakeThreadsService.forceVisible);

src/styles/sidebar/buttons.scss

@@ -34,3 +34,12 @@
     padding: var.$layout-space--small var.$layout-space;
   }
 }
+
+// An IconButton, but override minimum height/width on touch screen devices
+.NonResponsiveIconButton {
+  @include buttons.IconButton(
+    (
+      'responsive': false,
+    )
+  );
+}

src/styles/sidebar/components/Thread.scss

-@use "../../mixins/buttons";
 @use "../../mixins/layout";
 @use "../../variables" as var;
 
@@ -13,19 +12,17 @@
     margin-left: var.$layout-space;
   }
 
-  &__children {
-    margin-left: -1 * var.$layout-space;
-  }
-
-  &__unavailable-message {
-    margin: 0 var.$layout-space;
-  }
-
   // Left "channel" of thread
   &__collapse {
-    margin-right: 1em;
+    position: relative;
+    // Ensure that even when this thread is collapsed, it is allotted a minimal
+    // bit of vertical real estate so that the expand/collapse toggle (which is
+    // positioned absolute) has "room". This applies when collapsing a thread
+    // with a deleted annotation in it, as otherwise there is no content when
+    // collapsed.
+    min-height: 2em;
     border-right: 1px dashed var.$color-border;
-    // The entire channel is NOT clickable so don't make it look like it is
+    // The entire channel is not clickable so don't make it look like it is
     // (overrides `pointer` cursor applied to entire card)
     cursor: auto;
 
@@ -39,30 +36,23 @@
     }
   }
 
-  &__collapse-button {
-    @include buttons.button;
-    color: var.$grey-mid;
-    margin-right: -1.25em;
-    padding: 0.25em 0.75em 0.75em 0.75em;
-    // Need a non-transparent background so that the dashed border line
-    // does not show through the button
+  // Container holding the thread's collapse/expand "chevron" icon button
+  &__collapse-button-container {
+    position: absolute;
+    // Position this element (and its button) such that it is horizontally
+    // centered on the parent element's right border and aligned vertically
+    // with the content on the right
+    top: -0.25em;
+    left: -1em;
+    // Give a non-transparent background to this element so that the dashed
+    // border (vertical) on the parent element doesn't show through the
+    // child button
     background-color: var.$white;
-
-    svg {
-      // This is not an icon and as such does not use a mixin
-      width: 12px;
-      height: 12px;
-      color: var.$grey-4;
   }
 
-    &:hover &__icon {
-      color: var.$grey-6;
-    }
-  }
-  &__hidden-toggle-button {
-    // This makes the vertical alignment with thread-collapse chevrons
-    // more precise
-    @include buttons.button--labeled;
+  &__hidden-toggle-button-container {
+    // This makes the vertical alignment of the "Show x more in conversation"
+    // button more precise with thread-collapse chevrons
     margin-top: -0.25em;
   }