Minor CR fixups

 - Use a variable instead of a hardcoded color for the "New note" button
   in the sidebar tutorial.
 - Remove unused `width` and `height` attributes. The icon's size is set
   via `width` and `height` properties in CSS.

src/sidebar/templates/sidebar-tutorial.html

@@ -53,7 +53,7 @@
       <div class="sidebar-tutorial__list-item-content">
         Select some text to
           <span class="sidebar-tutorial__list-item-annotate">annotate</span>
-          <svg-icon width="3px" height="10px" class="sidebar-tutorial__list-item-cursor" name="'cursor'"></svg-icon>
+          <svg-icon class="sidebar-tutorial__list-item-cursor" name="'cursor'"></svg-icon>
         or highlight.
       </div>
     </li>

src/styles/sidebar-tutorial.scss

@@ -76,7 +76,7 @@
 }
 
 .sidebar-tutorial__list-item-new-note-btn {
-  background-color: #626262;
+  background-color: $color-dove-gray;
   border: none;
   border-radius: 3px;
   color: #fff;