added tooltips like the new note button (and consequently extracted some buttons and styles)

browser/main/SideNav/ListButton.js

@@ -0,0 +1,24 @@
+import PropTypes from 'prop-types'
+import React from 'react'
+import CSSModules from 'browser/lib/CSSModules'
+import styles from './SwitchButton.styl'
+
+const ListButton = ({
+  onClick, isTagActive
+}) => (
+  <button styleName={isTagActive ? 'non-active-button' : 'active-button'} onClick={onClick}>
+    <img src={isTagActive
+        ? '../resources/icon/icon-list.svg'
+        : '../resources/icon/icon-list-active.svg'
+    }
+    />
+    <span styleName='tooltip'>Notes</span>
+  </button>
+)
+
+ListButton.propTypes = {
+  onClick: PropTypes.func.isRequired,
+  isTagActive: PropTypes.bool.isRequired
+}
+
+export default CSSModules(ListButton, styles)

browser/main/SideNav/PreferenceButton.js

@@ -0,0 +1,19 @@
+import PropTypes from 'prop-types'
+import React from 'react'
+import CSSModules from 'browser/lib/CSSModules'
+import styles from './PreferenceButton.styl'
+
+const PreferenceButton = ({
+  onClick
+}) => (
+  <button styleName='top-menu-preference' onClick={(e) => onClick(e)}>
+    <img styleName='iconTag' src='../resources/icon/icon-setting.svg' />
+    <span styleName='tooltip'>Preferences</span>
+  </button>
+)
+
+PreferenceButton.propTypes = {
+  onClick: PropTypes.func.isRequired
+}
+
+export default CSSModules(PreferenceButton, styles)

browser/main/SideNav/PreferenceButton.styl

@@ -0,0 +1,51 @@
+.top-menu-preference
+  navButtonColor()
+  position absolute
+  top 22px
+  right 10px
+  width 2em
+  background-color transparent
+  &:hover
+    color $ui-button-default--active-backgroundColor
+    background-color transparent
+    .tooltip
+      opacity 1
+  &:active, &:active:hover
+    color $ui-button-default--active-backgroundColor
+
+body[data-theme="white"]
+  .top-menu-preference
+    navWhiteButtonColor()
+    background-color transparent
+    &:hover
+      color #0B99F1
+      background-color transparent
+    &:active, &:active:hover
+      color #0B99F1
+      background-color transparent
+
+body[data-theme="dark"]
+  .top-menu-preference
+    navDarkButtonColor()
+    background-color transparent
+    &:active
+      background-color alpha($ui-dark-button--active-backgroundColor, 20%)
+      background-color transparent
+    &:hover
+      background-color alpha($ui-dark-button--active-backgroundColor, 20%)
+      background-color transparent
+
+
+
+.tooltip
+  tooltip()
+  position absolute
+  pointer-events none
+  top 26px
+  left -20px
+  z-index 200
+  padding 5px
+  line-height normal
+  border-radius 2px
+  opacity 0
+  transition 0.1s

browser/main/SideNav/SideNav.styl

@@ -11,19 +11,6 @@
 .top
   padding-bottom 15px
 
-.top-menu-preference
-  navButtonColor()
-  position absolute
-  top 22px
-  right 10px
-  width 2em
-  background-color transparent
-  &:hover
-    color $ui-button-default--active-backgroundColor
-    background-color transparent
-  &:active, &:active:hover
-    color $ui-button-default--active-backgroundColor
-
 .switch-buttons
   background-color transparent
   border 0
@@ -31,21 +18,7 @@
   display flex
   text-align center
 
-.non-active-button
-  color $ui-inactive-text-color
-  font-size 16px
-  border 0
-  background-color transparent
-  transition 0.2s
-  display flex
-  text-align center
-  margin-right 4px;
-  &:hover
-    color alpha(#239F86, 60%)
 
-.active-button
-  @extend .non-active-button
-  color $ui-button-default--active-backgroundColor
   
 .top-menu-label
   margin-left 5px
@@ -109,33 +82,6 @@ body[data-theme="white"]
     background-color #f9f9f9
     color $ui-text-color
 
-  .top-menu-preference
-    navWhiteButtonColor()
-    background-color transparent
-    &:hover
-      color #0B99F1
-      background-color transparent
-    &:active, &:active:hover
-      color #0B99F1
-      background-color transparent
-
-  .non-active-button
-    color $ui-inactive-text-color
-    &:hover
-      color alpha(#0B99F1, 60%)
-
-  .tag-title
-    p
-      color $ui-text-color
-
-  .non-active-button
-    &:hover
-      color alpha(#0B99F1, 60%)
-
-  .active-button
-    @extend .non-active-button
-    color #0B99F1
-
 body[data-theme="dark"]
   .root, .root--folded
     border-right 1px solid $ui-dark-borderColor
@@ -145,25 +91,6 @@ body[data-theme="dark"]
   .top
     border-color $ui-dark-borderColor
 
-  .top-menu-preference
-    navDarkButtonColor()
-    background-color transparent
-    &:active
-      background-color alpha($ui-dark-button--active-backgroundColor, 20%)
-      background-color transparent
-    &:hover
-      background-color alpha($ui-dark-button--active-backgroundColor, 20%)
-      background-color transparent
-
-  .non-active-button
-    color alpha($ui-dark-text-color, 60%)
-    &:hover
-      color alpha(#0B99F1, 60%)
-
-  .tag-title
-    p
-      color alpha($ui-dark-text-color, 60%)
-
 body[data-theme="solarized-dark"]
   .root, .root--folded
     background-color $ui-solarized-dark-backgroundColor

browser/main/SideNav/SwitchButton.styl

@@ -0,0 +1,59 @@
+.non-active-button
+  color $ui-inactive-text-color
+  font-size 16px
+  border 0
+  background-color transparent
+  transition 0.2s
+  display flex
+  text-align center
+  margin-right 4px
+  position relative
+  &:hover
+    color alpha(#239F86, 60%)
+    .tooltip
+      opacity 1
+
+.active-button
+  @extend .non-active-button
+  color $ui-button-default--active-backgroundColor
+
+.tooltip
+  tooltip()
+  position absolute
+  pointer-events none
+  top 22px
+  left -2px
+  z-index 200
+  padding 5px
+  line-height normal
+  border-radius 2px
+  opacity 0
+  transition 0.1s
+
+body[data-theme="white"]
+  .non-active-button
+    color $ui-inactive-text-color
+    &:hover
+      color alpha(#0B99F1, 60%)
+
+  .tag-title
+    p
+      color $ui-text-color
+
+  .non-active-button
+    &:hover
+      color alpha(#0B99F1, 60%)
+
+  .active-button
+    @extend .non-active-button
+    color #0B99F1
+
+body[data-theme="dark"]
+  .non-active-button
+    color alpha($ui-dark-text-color, 60%)
+    &:hover
+      color alpha(#0B99F1, 60%)
+
+  .tag-title
+    p
+      color alpha($ui-dark-text-color, 60%)

browser/main/SideNav/TagButton.js

@@ -0,0 +1,24 @@
+import PropTypes from 'prop-types'
+import React from 'react'
+import CSSModules from 'browser/lib/CSSModules'
+import styles from './SwitchButton.styl'
+
+const TagButton = ({
+  onClick, isTagActive
+}) => (
+  <button styleName={isTagActive ? 'active-button' : 'non-active-button'} onClick={onClick}>
+    <img src={isTagActive
+        ? '../resources/icon/icon-tag-active.svg'
+        : '../resources/icon/icon-tag.svg'
+    }
+    />
+    <span styleName='tooltip'>Tags</span>
+  </button>
+)
+
+TagButton.propTypes = {
+  onClick: PropTypes.func.isRequired,
+  isTagActive: PropTypes.bool.isRequired
+}
+
+export default CSSModules(TagButton, styles)

browser/main/SideNav/index.js

@@ -11,6 +11,9 @@ import SideNavFilter from 'browser/components/SideNavFilter'
 import StorageList from 'browser/components/StorageList'
 import NavToggleButton from 'browser/components/NavToggleButton'
 import EventEmitter from 'browser/main/lib/eventEmitter'
+import PreferenceButton from './PreferenceButton'
+import ListButton from './ListButton'
+import TagButton from './TagButton'
 
 class SideNav extends React.Component {
   // TODO: should not use electron stuff v0.7
@@ -162,27 +165,11 @@ class SideNav extends React.Component {
       >
         <div styleName='top'>
           <div styleName='switch-buttons'>
-            <button styleName={isTagActive ? 'non-active-button' : 'active-button'} onClick={this.handleSwitchFoldersButtonClick.bind(this)}>
-              <img src={isTagActive
-                  ? '../resources/icon/icon-list.svg'
-                  : '../resources/icon/icon-list-active.svg'
-                }
-              />
-            </button>
-            <button styleName={isTagActive ? 'active-button' : 'non-active-button'} onClick={this.handleSwitchTagsButtonClick.bind(this)}>
-              <img src={isTagActive
-                  ? '../resources/icon/icon-tag-active.svg'
-                  : '../resources/icon/icon-tag.svg'
-                }
-              />
-            </button>
+            <ListButton onClick={this.handleSwitchFoldersButtonClick.bind(this)} isTagActive={isTagActive} />
+            <TagButton onClick={this.handleSwitchTagsButtonClick.bind(this)} isTagActive={isTagActive} />
           </div>
           <div>
-            <button styleName='top-menu-preference'
-              onClick={(e) => this.handleMenuButtonClick(e)}
-            >
-              <img styleName='iconTag' src='../resources/icon/icon-setting.svg' />
-            </button>
+            <PreferenceButton onClick={this.handleMenuButtonClick} />
           </div>
         </div>
         {this.SideNavComponent(isFolded, storageList)}