MM-61318 Don't apply extra CSS to Markdown headings in thread list (#29138)

webapp/channels/src/components/threading/global_threads/thread_item/__snapshots__/thread_item.test.tsx.snap

@@ -7,7 +7,7 @@ exports[`components/threading/global_threads/thread_item should report total num
   onClick={[Function]}
   tabIndex={0}
 >
-  <h1>
+  <header>
     <div
       className="ThreadItem__author"
     >
@@ -35,7 +35,7 @@ exports[`components/threading/global_threads/thread_item should report total num
       }
       useTime={false}
     />
-  </h1>
+  </header>
   <div
     className="menu-anchor alt-visible"
   >
@@ -123,7 +123,7 @@ exports[`components/threading/global_threads/thread_item should report unread me
   onClick={[Function]}
   tabIndex={0}
 >
-  <h1>
+  <header>
     <div
       className="indicator"
     >
@@ -160,7 +160,7 @@ exports[`components/threading/global_threads/thread_item should report unread me
       }
       useTime={false}
     />
-  </h1>
+  </header>
   <div
     className="menu-anchor alt-visible"
   >
@@ -248,7 +248,7 @@ exports[`components/threading/global_threads/thread_item should report unread me
   onClick={[Function]}
   tabIndex={0}
 >
-  <h1>
+  <header>
     <div
       className="indicator"
     >
@@ -283,7 +283,7 @@ exports[`components/threading/global_threads/thread_item should report unread me
       }
       useTime={false}
     />
-  </h1>
+  </header>
   <div
     className="menu-anchor alt-visible"
   >

webapp/channels/src/components/threading/global_threads/thread_item/thread_item.scss

@@ -105,7 +105,7 @@
         place-content: center;
     }
 
-    h1 {
+    > header {
         position: relative;
         display: grid;
         margin: 0 0 6px;
@@ -117,6 +117,14 @@
         justify-items: start;
         line-height: 20px;
         white-space: nowrap;
+
+        > time {
+            color: rgba(var(--center-channel-color-rgb), 0.75);
+            font-size: 12px;
+            font-weight: normal;
+            grid-column: 3/4;
+            line-height: 20px;
+        }
     }
 
     div.preview {
@@ -127,14 +135,6 @@
         @include mixins.text-clamp(2, 20);
     }
 
-    time {
-        color: rgba(var(--center-channel-color-rgb), 0.75);
-        font-size: 12px;
-        font-weight: normal;
-        grid-column: 3/4;
-        line-height: 20px;
-    }
-
     .menu-anchor {
         position: absolute;
         top: 12px;

webapp/channels/src/components/threading/global_threads/thread_item/thread_item.tsx

@@ -182,7 +182,7 @@ function ThreadItem({
             id={isFirstThreadInList ? 'tutorial-threads-mobile-list' : ''}
             onClick={selectHandler}
         >
-            <h1>
+            <header>
                 {Boolean(newMentions || newReplies) && (
                     <div className='indicator'>
                         {newMentions ? (
@@ -217,7 +217,7 @@ function ThreadItem({
                     className='alt-hidden'
                     value={lastReplyAt}
                 />
-            </h1>
+            </header>
             <div className='menu-anchor alt-visible'>
                 <ThreadMenu
                     threadId={threadId}