added scss files

chrome/common/extensions/docs/static/sass/_layout.scss

+@mixin content-container-layout {
+  margin: auto;
+  width: 90%;
+}
+
+//-----------------------------------------------------------------------
+// Layout
+//-----------------------------------------------------------------------
+
+* {
+  padding: 0;
+  margin: 0;
+  @include box-sizing(border-box);
+}
+
+html, body {
+  overflow-x: hidden; // Allows .span-full to take up entire viewport without overflowing.
+  overflow-y: auto;
+}
+
+img {
+  max-width: 100%;
+}  
+
+#gc-container {
+  max-width: $site-max-width;
+  @include content-container-layout();
+}
+
+#gc-pagecontent {
+  > .g-section {
+    margin: $main-content-top-margin 0;
+  }
+}
+
+main {
+  margin-bottom: 50px;
+  position: relative;
+}
+
+footer[role="contentinfo"] {
+  padding: 40px 0 50px;
+}
+
+// Phone
+@media only screen and (max-width: $break-small)  { 
+  #gc-container {
+    width: auto;
+  }
+  #gc-pagecontent {
+    @include content-container-layout();
+
+    > .g-section {
+      margin: $main-content-top-margin / 2 0;
+    }
+  }
+  footer[role="contentinfo"]  {
+    padding: $main-content-top-margin / 2 $main-content-top-margin - 10;
+  }
+}
+
+// Tablet
+@media only screen and (min-width: $break-small + 1) and (max-width: $break-large) { 
+  #gc-container {
+    width: 95%;
+  }
+}
+
+@media only screen and (min-width: $break-large)  { 
+
+}