DevTools: added "overlayContents" mode, where DevTools content is placed around and underneath inse…

Source/devtools/front_end/helpScreen.css

 .help-window-outer {
     position: absolute;
     top: 0;
     left: 0;
     right: 0;
     bottom: 0;
     z-index: 2000;
 }
 
 .help-window-main {
@@ skipping 277 matching lines @@
     left: 15px;
     right: 0;
     bottom: 0;
     overflow: auto;
 }
 
 #settings-screen .tabbed-pane-header {
     border: none transparent;
     height: auto;
     width: 110px;
-    position: relative;
-    top: 14px;
+    margin-top: 14px;
     flex: auto;
 }
 
 #settings-screen .tabbed-pane-header-contents {
     margin: 0;
 }
 
 #settings-screen .tabbed-pane-header-tabs {
     display: flex;
     flex-direction: column;
@@ skipping 363 matching lines @@
     -webkit-box-pack: center;
     display: -webkit-box;
     z-index: 2000 !important;
     padding: 5px;
     background-color: rgba(255, 255, 255, 0.4) !important;
 }
 
 #overrides-tab-content .help-container {
     -webkit-column-width: auto !important;
 }