fix(plugins/plugin-client-common): h2 in Notebooks have double underline

Fixes #5574

Author: starpit

plugins/plugin-client-common/web/scss/components/Terminal/Commentary.scss

@@ -24,15 +24,30 @@
   }
 }
 
-@mixin MajorHeaders {
+@mixin h1 {
+  @include Card {
+    h1 {
+      @content;
+    }
+  }
+}
+
+@mixin h2 {
   @include Card {
-    h1,
     h2 {
       @content;
     }
   }
 }
 
+@mixin h3 {
+  @include Card {
+    h3 {
+      @content;
+    }
+  }
+}
+
 @mixin Paragraphs {
   @include Card {
     p {
@@ -50,14 +65,25 @@
 }
 
 @include Scrollback {
-  @include MajorHeaders {
+  @include h1 {
     font-weight: 500;
     font-size: 2.125rem;
     letter-spacing: 0.32px;
     padding: 0.5rem 1rem 0.5rem 0.25rem;
     border-bottom: 1px solid var(--color-table-border2);
   }
 
+  @include h2 {
+    font-weight: 400;
+    font-size: 1.5rem;
+    letter-spacing: 0.32px;
+    margin: 0 0 0.5rem;
+
+    &:before {
+      display: none;
+    }
+  }
+
   @include Paragraphs {
     font-size: 1rem;
     line-height: 1.5rem;