--- a/devtools/client/debugger/new/dist/debugger.css
+++ b/devtools/client/debugger/new/dist/debugger.css
@@ -516,31 +516,29 @@ menuseparator {
   box-sizing: border-box;
 
   /* Positive z-index positions the splitter on top of its siblings and makes
      it clickable on both sides. */
   z-index: 1;
 }
 
 .split-box.vert > .splitter {
-  min-width: calc(var(--devtools-splitter-inline-start-width) +
-    var(--devtools-splitter-inline-end-width) + 1px);
+  min-width: var(--devtools-vertical-splitter-min-width);
 
   border-left-width: var(--devtools-splitter-inline-start-width);
   border-right-width: var(--devtools-splitter-inline-end-width);
 
   margin-left: calc(-1 * var(--devtools-splitter-inline-start-width) - 1px);
   margin-right: calc(-1 * var(--devtools-splitter-inline-end-width));
 
   cursor: ew-resize;
 }
 
 .split-box.horz > .splitter {
-  min-height: calc(var(--devtools-splitter-top-width) +
-    var(--devtools-splitter-bottom-width) + 1px);
+  min-height: var(--devtools-horizontal-splitter-min-height);
 
   border-top-width: var(--devtools-splitter-top-width);
   border-bottom-width: var(--devtools-splitter-bottom-width);
 
   margin-top: calc(-1 * var(--devtools-splitter-top-width) - 1px);
   margin-bottom: calc(-1 * var(--devtools-splitter-bottom-width));
 
   cursor: ns-resize;

--- a/devtools/client/shared/components/splitter/SplitBox.css
+++ b/devtools/client/shared/components/splitter/SplitBox.css
@@ -43,41 +43,47 @@
   box-sizing: border-box;
 
   /* Positive z-index positions the splitter on top of its siblings and makes
      it clickable on both sides. */
   z-index: 1;
 }
 
 .split-box.vert > .splitter {
-  min-width: calc(var(--devtools-splitter-inline-start-width) +
-    var(--devtools-splitter-inline-end-width) + 1px);
+  min-width: var(--devtools-vertical-splitter-min-width);
 
   border-inline-start-width: var(--devtools-splitter-inline-start-width);
   border-inline-end-width: var(--devtools-splitter-inline-end-width);
 
   margin-inline-start: calc(-1 * var(--devtools-splitter-inline-start-width) - 1px);
   margin-inline-end: calc(-1 * var(--devtools-splitter-inline-end-width));
 
   cursor: ew-resize;
 }
 
 .split-box.horz > .splitter {
-  min-height: calc(var(--devtools-splitter-top-width) +
-    var(--devtools-splitter-bottom-width) + 1px);
+  /* Emphasize the horizontal splitter width and color */
+  min-height: var(--devtools-emphasized-horizontal-splitter-min-height);
+
+  background-color: var(--theme-emphasized-splitter-color);
 
   border-top-width: var(--devtools-splitter-top-width);
   border-bottom-width: var(--devtools-splitter-bottom-width);
 
   margin-top: calc(-1 * var(--devtools-splitter-top-width) - 1px);
   margin-bottom: calc(-1 * var(--devtools-splitter-bottom-width));
 
   cursor: ns-resize;
 }
 
+/* Emphasized splitter has the hover style. */
+.split-box.horz > .splitter:hover {
+  background-color: var(--theme-emphasized-splitter-color-hover);
+}
+
 .split-box.disabled {
   pointer-events: none;
 }
 
 /**
  * Make sure splitter panels are not processing any mouse
  * events. This is good for performance during splitter
  * bar dragging.

--- a/devtools/client/themes/splitters.css
+++ b/devtools/client/themes/splitters.css
@@ -3,26 +3,40 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 /* This file is loaded by both browser.xul and toolbox.xul. Therefore, rules
    defined here can not rely on toolbox.xul variables. */
 
 /* Splitters */
 
 :root {
+  /* Draggable splitter element size */
+  --devtools-splitter-element-size: 1px;
+  --devtools-emphasized-splitter-element-size: 2px;
+
   /* Define the widths of the draggable areas on each side of a splitter. top
      and bottom widths are used for horizontal splitters, inline-start and
      inline-end for side splitters.*/
 
   --devtools-splitter-top-width: 2px;
   --devtools-splitter-bottom-width: 2px;
+  --devtools-horizontal-splitter-min-height: calc(var(--devtools-splitter-top-width) +
+                                                  var(--devtools-splitter-bottom-width) +
+                                                  var(--devtools-splitter-element-size));
+  --devtools-emphasized-horizontal-splitter-min-height: calc(var(--devtools-splitter-top-width) +
+                                                             var(--devtools-splitter-bottom-width) +
+                                                             var(--devtools-emphasized-splitter-element-size));
 
   /* Small draggable area on inline-start to avoid overlaps on scrollbars.*/
   --devtools-splitter-inline-start-width: 1px;
   --devtools-splitter-inline-end-width: 4px;
+
+  --devtools-vertical-splitter-min-width: calc(var(--devtools-splitter-inline-start-width) +
+                                               var(--devtools-splitter-inline-end-width) +
+                                               var(--devtools-splitter-element-size));
 }
 
 #appcontent[devtoolstheme="light"] {
   /* These variables are used in browser.xul but inside the toolbox they are overridden by --theme-splitter-color */
   --devtools-splitter-color: #dde1e4;
 }
 
 #appcontent[devtoolstheme="dark"] {
@@ -43,31 +57,41 @@ splitter.devtools-horizontal-splitter,
   box-sizing: border-box;
 
   /* Positive z-index positions the splitter on top of its siblings and makes
      it clickable on both sides. */
   z-index: 1;
 }
 
 splitter.devtools-horizontal-splitter {
-  min-height: calc(var(--devtools-splitter-top-width) +
-    var(--devtools-splitter-bottom-width) + 1px);
+  min-height: var(--devtools-horizontal-splitter-min-height);
 
   border-top-width: var(--devtools-splitter-top-width);
   border-bottom-width: var(--devtools-splitter-bottom-width);
 
   margin-top: calc(-1 * var(--devtools-splitter-top-width) - 1px);
   margin-bottom: calc(-1 * var(--devtools-splitter-bottom-width));
 
   cursor: ns-resize;
 }
 
+#toolbox-deck + splitter.devtools-horizontal-splitter {
+  min-height: var(--devtools-emphasized-horizontal-splitter-min-height);
+}
+
+/**
+ * Emphasized splitter has the hover style.
+ * This emphasized splitter affect splitter console only.
+ */
+#toolbox-deck + splitter.devtools-horizontal-splitter:hover {
+  background-color: var(--theme-emphasized-splitter-color-hover);
+}
+
 .devtools-side-splitter {
-  min-width: calc(var(--devtools-splitter-inline-start-width) +
-    var(--devtools-splitter-inline-end-width) + 1px);
+  min-width: var(--devtools-vertical-splitter-min-width);
 
   border-inline-start-width: var(--devtools-splitter-inline-start-width);
   border-inline-end-width: var(--devtools-splitter-inline-end-width);
 
   margin-inline-start: calc(-1 * var(--devtools-splitter-inline-start-width) - 1px);
   margin-inline-end: calc(-1 * var(--devtools-splitter-inline-end-width));
 
   cursor: ew-resize;

--- a/devtools/client/themes/variables.css
+++ b/devtools/client/themes/variables.css
@@ -36,16 +36,18 @@
   --theme-selection-background: var(--blue-55);
   --theme-selection-background-hover: #F0F9FE;
   --theme-selection-focus-background: var(--toolbarbutton-hover-background);
   --theme-selection-focus-color: var(--grey-70);
   --theme-selection-color: #ffffff;
 
   /* Border color that splits the toolbars/panels/headers. */
   --theme-splitter-color: #e0e0e1;
+  --theme-emphasized-splitter-color: var(--grey-30);
+  --theme-emphasized-splitter-color-hover: var(--grey-40);
 
   --theme-comment: var(--grey-50);
   --theme-comment-alt: #ccd1d5;
 
   --theme-body-color: var(--grey-60);
   --theme-body-color-alt: var(--grey-40);
   --theme-body-color-inactive: #999797;
   --theme-content-color1: #292e33;
@@ -144,16 +146,18 @@
   --theme-selection-background: #204E8A;
   --theme-selection-background-hover: #353B48;
   --theme-selection-focus-background: var(--grey-60);
   --theme-selection-focus-color: var(--grey-30);
   --theme-selection-color: #ffffff;
 
   /* Border color that splits the toolbars/panels/headers. */
   --theme-splitter-color: #3c3c3d;
+  --theme-emphasized-splitter-color: var(--gery-60);
+  --theme-emphasized-splitter-color-hover: var(--grey-50);
 
   --theme-comment: #939393;
   --theme-comment-alt: #939393;
 
   --theme-body-color: #909090;
   --theme-body-color-alt: var(--grey-50);
   --theme-body-color-inactive: var(--grey-40);
   --theme-content-color1: var(--grey-30);