Remove src/styles/base.scss

This module was used by multiple SASS entry points (annotator, sidebar)
even though each mixin or class within it was either trivial or only
actually used by one of the entry points. Moving the mixins to the
individual entry points will make it easier to run the migrator.

src/styles/annotator/annotator.scss

 @import '../variables';
-@import '../base';
 @import '../mixins/icons';
 @import '../mixins/focus';
+@import '../mixins/shadow';
 
 @import './adder';
 
@@ -46,7 +46,7 @@ $base-font-size: 14px;
   // frame styles
   @import './bucket-bar';
   user-select: none;
-  @include grey-background;
+  background: $grey-2;
   direction: ltr;
   background: none;
   font-size: $base-font-size;
@@ -172,6 +172,11 @@ $base-font-size: 14px;
   transition: none !important;
 }
 
+.annotator-hide {
+  display: none;
+  visibility: hidden;
+}
+
 /*
   Mobile layout
   240-479 px

src/styles/base.scss

-/* Style input placeholders */
-@mixin placeholder {
-  &.placeholder {
-    @content;
-  }
-  &:placeholder {
-    @content;
-  }
-  &::placeholder {
-    @content;
-  }
-}
-
-/* Shadow mixins */
-@mixin smallshadow($a: 0, $b: 1px, $c: 0.1) {
-  box-shadow: $a $b 1px hsla(0, 0%, 0%, $c);
-}
-
-@mixin quote {
-  @include font-normal;
-
-  border-left: 3px solid $gray-lighter;
-  color: $grey-4;
-  font-family: sans-serif;
-  font-size: 12px;
-  font-style: italic;
-  letter-spacing: 0.1px;
-  padding: 0 1em;
-}
-
-//Provides the grey-background
-@mixin grey-background {
-  background: $grey-2;
-}
-
-.annotator-hide {
-  display: none;
-  visibility: hidden;
-}

src/styles/mixins/forms.scss

+/* Style input placeholders */
+@mixin placeholder {
+  &.placeholder {
+    @content;
+  }
+  &:placeholder {
+    @content;
+  }
+  &::placeholder {
+    @content;
+  }
+}
+
 // See http://compass-style.org/reference/compass/utilities/general/clearfix/#mixin-pie-clearfix
 @mixin pie-clearfix {
   &:after {

src/styles/mixins/shadow.scss

+@mixin smallshadow($a: 0, $b: 1px, $c: 0.1) {
+  box-shadow: $a $b 1px hsla(0, 0%, 0%, $c);
+}

src/styles/sidebar/components/annotation.scss

+@mixin quote {
+  @include font-normal;
+
+  border-left: 3px solid $gray-lighter;
+  color: $grey-4;
+  font-family: sans-serif;
+  font-size: 12px;
+  font-style: italic;
+  letter-spacing: 0.1px;
+  padding: 0 1em;
+}
+
 // Highlight quote of annotation whenever its thread is hovered
 .thread-list__card:hover .annotation-quote {
   border-left: $highlight 3px solid;

src/styles/sidebar/sidebar.scss

@@ -17,7 +17,6 @@ $base-line-height: 20px;
 
 // Misc. legacy :(
 // ---------------
-@import '../base';
 @import '../forms';
 @import './styled-text';
 @import './common';
@@ -69,8 +68,7 @@ body {
 }
 
 body {
-  @include grey-background;
-
+  background: $grey-2;
   font-family: $sans-font-family;
   font-weight: normal;
   -webkit-overflow-scrolling: touch;
@@ -84,8 +82,7 @@ hypothesis-app {
 .app-content-wrapper {
   $sidebar-h-padding: 9px;
 
-  @include grey-background;
-
+  background: $grey-2;
   min-height: 100%;
   height: 100%;
   overflow: scroll;