[DevTools] Initial implementation of device modes.

Source/devtools/front_end/emulation/responsiveDesignView.css

Index: Source/devtools/front_end/emulation/responsiveDesignView.css
diff --git a/Source/devtools/front_end/emulation/responsiveDesignView.css b/Source/devtools/front_end/emulation/responsiveDesignView.css
index ce20a334fb35f186f22695d5defd3a3f4f303ac4..fe3f9b2f5164369258be952158a0a0c0f5e0607f 100644
--- a/Source/devtools/front_end/emulation/responsiveDesignView.css
+++ b/Source/devtools/front_end/emulation/responsiveDesignView.css
@@ -82,6 +82,10 @@
     transform: rotate(90deg);
 }
 
+.responsive-design-page-container {
+    background-color: #171717;
+}
+
 .responsive-design-page-scale-container {
     position: absolute !important;
     top: 0;
@@ -218,6 +222,7 @@
 
 .responsive-design-toolbar label {
     cursor: default !important;
+    margin: 0 2px;
 }
 
 .responsive-design-toolbar input[type='text'] {
@@ -302,6 +307,7 @@ div.responsive-design-icon:disabled {
 
 .responsive-design-icon-swap {
     margin-left: 1px;
+    top: 4px;
 }
 
 .responsive-design-icon-swap:hover {
@@ -352,8 +358,25 @@ div.responsive-design-icon:disabled {
     margin-left: 0;
 }
 
-.responsive-design-section-device select {
-    width: 283px;
+.responsive-design-section-device .device-select {
+    width: 140px;
+}
+
+.responsive-design-section-device .mode-container {
+    display: inline-block;
+    width: 150px;
+    padding: 0 10px;
+}
+
+.responsive-design-section-device .mode-select select {
+    width: 116px;
+}
+
+.responsive-design-section-device .mode-select label {
+    margin-left: 4px;
+    color: rgb(255, 156, 0);
+    position: relative;
+    top: 1px;
 }
 
 .responsive-design-section-device input[type='text'],