diff --git a/gtk-3.0/_common.scss b/gtk-3.0/_common.scss
index 36ade907..99963742 100644
--- a/gtk-3.0/_common.scss
+++ b/gtk-3.0/_common.scss
@@ -2039,6 +2039,8 @@ notebook {
   &.frame {
     border-style: none;
 
+    > header { margin-left: 0; }
+
     > stack:not(:only-child) { // the :not(:only-child) is for "hidden" notebooks
       border: 1px solid shade($bg_color, 0.9);
     }
@@ -2304,9 +2306,16 @@ notebook {
     }
   }
 
+  // if the notebook property show_border is set to false, the frame directly inside the notebook
+  // doesn't exist, so we define the tab margins, the background and backdrop colors here:
+
+  > header {
+    margin-left: 6px;
+  }
+
   > stack:not(:only-child) { // the :not(:only-child) is for "hidden" notebooks
     background-color: shade($bg_color, 1.05);
-    border-width: 1px;
+    border-width: 1px 0 0;
     border-color: shade($bg_color, 0.9);
     border-style: solid;
     &:backdrop { background-color: $backdrop_bg_color; }
diff --git a/gtk-3.0/gtk-contained-dark.css b/gtk-3.0/gtk-contained-dark.css
index 93744434..d1b3f76e 100644
--- a/gtk-3.0/gtk-contained-dark.css
+++ b/gtk-3.0/gtk-contained-dark.css
@@ -2360,6 +2360,9 @@ notebook.frame {
   notebook.frame > stack:not(:only-child) {
     border: 1px solid shade(#393f3f, 0.9); }
 
+notebook.frame > header {
+  margin-left: 0; }
+
 notebook > header {
   padding: 1px;
   background-color: #393f3f; }
@@ -2532,6 +2535,9 @@ notebook > header {
   notebook > header.right > tabs {
     margin-left: -2px; }
 
+notebook > header {
+  margin-left: 6px; }
+
 notebook > stack:not(:only-child) {
   background-color: shade(#393f3f, 1.05);
   border-width: 1px;
diff --git a/gtk-3.0/gtk-contained.css b/gtk-3.0/gtk-contained.css
index 19991a9c..8337f0d0 100644
--- a/gtk-3.0/gtk-contained.css
+++ b/gtk-3.0/gtk-contained.css
@@ -2374,6 +2374,9 @@ notebook.frame {
   notebook.frame > stack:not(:only-child) {
     border: 1px solid shade(#cecece, 0.9); }
 
+notebook.frame > header {
+  margin-left: 0; }
+
 notebook > header {
   padding: 1px;
   background-color: #cecece; }
@@ -2546,6 +2549,9 @@ notebook > header {
   notebook > header.right > tabs {
     margin-left: -2px; }
 
+notebook > header {
+  margin-left: 6px; }
+
 notebook > stack:not(:only-child) {
   background-color: shade(#cecece, 1.05);
   border-width: 1px;