added divider prop for Row, added story

added story with nested rows

added website example, added new story

renamed divider to the borderless, updated stories, code example

updated patch description

updated website example

refactored styles to use transparent token

applied same bg color for border color instead of making it transparent

moved back to border 0

.changeset/purple-olives-grin.md

@@ -0,0 +1,6 @@
+---
+'@shopify/polaris': patch
+'polaris.shopify.com': patch
+---
+
+Added `borderless` property to the `Row` component to determine whether the row should have visible `border-top`

polaris-react/src/components/IndexTable/IndexTable.module.scss

@@ -159,6 +159,10 @@ $loading-panel-height: 53px;
     cursor: auto;
   }
 
+  &.TableRow-borderless {
+    border: 0;
+  }
+
   &.toneSuccess {
     // stylelint-disable-next-line selector-max-combinators, selector-max-class, selector-max-specificity -- generated by polaris-migrator DO NOT COPY
     &,
@@ -264,6 +268,19 @@ $loading-panel-height: 53px;
       border-bottom: var(--p-border-width-025) solid var(--p-color-border);
       border-color: var(--p-color-border);
     }
+
+    // stylelint-disable-next-line selector-max-class -- makes subheader borders not visible
+    &.TableRow-borderless {
+      border: 0;
+      // stylelint-disable-next-line selector-max-combinators, selector-max-class, selector-max-specificity --  makes subheader borders not visible
+      &,
+      .TableCell:first-child,
+      .TableCell-first,
+      .TableCell-first + .TableCell,
+      .TableCell:last-child {
+        border: 0;
+      }
+    }
   }
 
   &.TableRow-child {