diff --git a/source/blender/editors/interface/interface_panel.c b/source/blender/editors/interface/interface_panel.c
index 072362492d8..9ef71f23e79 100644
--- a/source/blender/editors/interface/interface_panel.c
+++ b/source/blender/editors/interface/interface_panel.c
@@ -1355,56 +1355,51 @@ void UI_panel_category_draw_all(ARegion *region, const char *category_id_active)
   const int category_tabs_width = round_fl_to_int(UI_PANEL_CATEGORY_MARGIN_WIDTH * zoom);
   const float dpi_fac = UI_DPI_FAC;
   /* Padding of tabs around text. */
   const int tab_v_pad_text = round_fl_to_int(TABS_PADDING_TEXT_FACTOR * dpi_fac * zoom) + 2 * px;
   /* Padding between tabs. */
   const int tab_v_pad = round_fl_to_int(TABS_PADDING_BETWEEN_FACTOR * dpi_fac * zoom);
   bTheme *btheme = UI_GetTheme();
   const float tab_curve_radius = btheme->tui.wcol_tab.roundness * U.widget_unit * zoom;
   const int roundboxtype = is_left ? (UI_CNR_TOP_LEFT | UI_CNR_BOTTOM_LEFT) :
                                      (UI_CNR_TOP_RIGHT | UI_CNR_BOTTOM_RIGHT);
-  bool is_alpha;
   bool do_scaletabs = false;
 #ifdef USE_FLAT_INACTIVE
   bool is_active_prev = false;
 #endif
   float scaletabs = 1.0f;
   /* Same for all tabs. */
   /* Intentionally don't scale by 'px'. */
   const int rct_xmin = is_left ? v2d->mask.xmin + 3 : (v2d->mask.xmax - category_tabs_width);
   const int rct_xmax = is_left ? v2d->mask.xmin + category_tabs_width : (v2d->mask.xmax - 3);
   const int text_v_ofs = (rct_xmax - rct_xmin) * 0.3f;
 
   int y_ofs = tab_v_pad;
 
   /* Primary theme colors. */
-  uchar theme_col_back[4];
   uchar theme_col_text[3];
   uchar theme_col_text_hi[3];
 
   /* Tab colors. */
   uchar theme_col_tab_bg[4];
   float theme_col_tab_active[4];
   float theme_col_tab_inactive[4];
   float theme_col_tab_outline[4];
 
-  UI_GetThemeColor4ubv(TH_BACK, theme_col_back);
   UI_GetThemeColor3ubv(TH_TEXT, theme_col_text);
   UI_GetThemeColor3ubv(TH_TEXT_HI, theme_col_text_hi);
 
   UI_GetThemeColor4ubv(TH_TAB_BACK, theme_col_tab_bg);
   UI_GetThemeColor4fv(TH_TAB_ACTIVE, theme_col_tab_active);
   UI_GetThemeColor4fv(TH_TAB_INACTIVE, theme_col_tab_inactive);
   UI_GetThemeColor4fv(TH_TAB_OUTLINE, theme_col_tab_outline);
 
-  is_alpha = (region->overlap && (theme_col_back[3] != 255));
-
   BLF_enable(fontid, BLF_ROTATION);
   BLF_rotation(fontid, M_PI_2);
   // UI_fontstyle_set(&style->widget);
   ui_fontscale(&fstyle_points, aspect / (U.pixelsize * 1.1f));
   BLF_size(fontid, fstyle_points, U.dpi);
 
   /* Check the region type supports categories to avoid an assert
    * for showing 3D view panels in the properties space. */
   if ((1 << region->regiontype) & RGN_TYPE_HAS_CATEGORY_MASK) {
     BLI_assert(UI_panel_category_is_visible(region));
@@ -1433,49 +1428,48 @@ void UI_panel_category_draw_all(ARegion *region, const char *category_id_active)
       rcti *rct = &pc_dyn->rect;
       rct->ymin = ((rct->ymin - v2d->mask.ymax) * scaletabs) + v2d->mask.ymax;
       rct->ymax = ((rct->ymax - v2d->mask.ymax) * scaletabs) + v2d->mask.ymax;
     }
 
     do_scaletabs = true;
   }
 
   /* Begin drawing. */
   GPU_line_smooth(true);
-
-  uint pos = GPU_vertformat_attr_add(
-      immVertexFormat(), "pos", GPU_COMP_I32, 2, GPU_FETCH_INT_TO_FLOAT);
-  immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
+  uint pos;
 
   /* Draw the background. */
-  if (is_alpha) {
-    GPU_blend(GPU_BLEND_ALPHA);
-    immUniformColor4ubv(theme_col_tab_bg);
-  }
-  else {
+  if (!region->overlap) {
+    pos = GPU_vertformat_attr_add(
+        immVertexFormat(), "pos", GPU_COMP_I32, 2, GPU_FETCH_INT_TO_FLOAT);
+    immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
+
     immUniformColor3ubv(theme_col_tab_bg);
-  }
 
-  if (is_left) {
-    immRecti(
-        pos, v2d->mask.xmin, v2d->mask.ymin, v2d->mask.xmin + category_tabs_width, v2d->mask.ymax);
-  }
-  else {
-    immRecti(
-        pos, v2d->mask.xmax - category_tabs_width, v2d->mask.ymin, v2d->mask.xmax, v2d->mask.ymax);
-  }
+    if (is_left) {
+      immRecti(pos,
+               v2d->mask.xmin,
+               v2d->mask.ymin,
+               v2d->mask.xmin + category_tabs_width,
+               v2d->mask.ymax);
+    }
+    else {
+      immRecti(pos,
+               v2d->mask.xmax - category_tabs_width,
+               v2d->mask.ymin,
+               v2d->mask.xmax,
+               v2d->mask.ymax);
+    }
 
-  if (is_alpha) {
-    GPU_blend(GPU_BLEND_NONE);
+    immUnbindProgram();
   }
 
-  immUnbindProgram();
-
   LISTBASE_FOREACH (PanelCategoryDyn *, pc_dyn, &region->panels_category) {
     const rcti *rct = &pc_dyn->rect;
     const char *category_id = pc_dyn->idname;
     const char *category_id_draw = IFACE_(category_id);
     const int category_width = BLI_rcti_size_y(rct) - (tab_v_pad_text * 2);
     size_t category_draw_len = BLF_DRAW_STR_DUMMY_MAX;
 #if 0
     int category_width = BLF_width(fontid, category_id_draw, BLF_DRAW_STR_DUMMY_MAX);
 #endif
 
@@ -1499,21 +1493,21 @@ void UI_panel_category_draw_all(ARegion *region, const char *category_id_active)
                rct->ymax + (px * 3));
       immUnbindProgram();
     }
 
     is_active_prev = is_active;
 
     if (is_active)
 #endif
     {
       /* Draw filled rectangle and outline for tab. */
-      UI_draw_roundbox_corner_set(roundboxtype);
+      UI_draw_roundbox_corner_set(region->overlap ? UI_CNR_ALL : roundboxtype);
       UI_draw_roundbox_4fv(
           &(const rctf){
               .xmin = rct->xmin,
               .xmax = rct->xmax,
               .ymin = rct->ymin,
               .ymax = rct->ymax,
           },
           true,
           tab_curve_radius,
           is_active ? theme_col_tab_active : theme_col_tab_inactive);
@@ -1522,31 +1516,33 @@ void UI_panel_category_draw_all(ARegion *region, const char *category_id_active)
               .xmin = rct->xmin,
               .xmax = rct->xmax,
               .ymin = rct->ymin,
               .ymax = rct->ymax,
           },
           false,
           tab_curve_radius,
           theme_col_tab_outline);
 
       /* Disguise the outline on one side to join the tab to the panel. */
-      pos = GPU_vertformat_attr_add(
-          immVertexFormat(), "pos", GPU_COMP_I32, 2, GPU_FETCH_INT_TO_FLOAT);
-      immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
-
-      immUniformColor4fv(is_active ? theme_col_tab_active : theme_col_tab_inactive);
-      immRecti(pos,
-               is_left ? rct->xmax - px : rct->xmin,
-               rct->ymin + px,
-               is_left ? rct->xmax : rct->xmin + px,
-               rct->ymax - px);
-      immUnbindProgram();
+      if (!region->overlap) {
+        pos = GPU_vertformat_attr_add(
+            immVertexFormat(), "pos", GPU_COMP_I32, 2, GPU_FETCH_INT_TO_FLOAT);
+        immBindBuiltinProgram(GPU_SHADER_2D_UNIFORM_COLOR);
+
+        immUniformColor4fv(is_active ? theme_col_tab_active : theme_col_tab_inactive);
+        immRecti(pos,
+                 is_left ? rct->xmax - px : rct->xmin,
+                 rct->ymin + px,
+                 is_left ? rct->xmax : rct->xmin + px,
+                 rct->ymax - px);
+        immUnbindProgram();
+      }
     }
 
     /* Tab titles. */
 
     if (do_scaletabs) {
       category_draw_len = BLF_width_to_strlen(
           fontid, category_id_draw, category_draw_len, category_width, NULL);
     }
 
     BLF_position(fontid, rct->xmax - text_v_ofs, rct->ymin + tab_v_pad_text, 0.0f);