Refactor Dialog with Aphrodite

Closes #8984

Per 2dd92a9, dialog.less can be safely removed (as styles under 'menu' has been just copied).

Test Plan:
1. Open 'Import Browser Data...' from Bookmarks on the main menu
2. Open devtool
3. Make sure 'dialog' is styled properly

app/renderer/components/common/dialog.js

@@ -14,6 +14,9 @@ const KeyCodes = require('../../../common/constants/keyCodes')
 // Utils
 const cx = require('../../../../js/lib/classSet')
 
+const {StyleSheet, css} = require('aphrodite/no-important')
+const globalStyles = require('../styles/global')
+
 /**
  * Represents a popup dialog
  */
@@ -39,7 +42,7 @@ class Dialog extends ImmutableComponent {
 
   render () {
     return <div className={cx({
-      dialog: true,
+      [css(styles.dialog)]: true,
       [this.props.className]: !!this.props.className
     })}
       data-test-id={this.props.testId}
@@ -64,4 +67,19 @@ Dialog.propTypes = {
   onHide: PropTypes.func
 }
 
+const styles = StyleSheet.create({
+  dialog: {
+    position: 'absolute',
+    top: 0,
+    left: 0,
+    height: '100%',
+    width: '100%',
+    zIndex: globalStyles.zindex.zindexDialogs,
+    display: 'flex',
+    justifyContent: 'center',
+    alignItems: 'center',
+    background: 'rgba(0, 0, 0, 0.15)'
+  }
+})
+
 module.exports = Dialog

js/entry.js

@@ -12,7 +12,6 @@ require('../less/forms.less')
 require('../less/switchControls.less')
 require('../less/tabs.less')
 require('../less/findbar.less')
-require('../less/dialogs.less')
 require('../less/downloadBar.less')
 require('../less/bookmarksToolbar.less')
 require('../less/notificationBar.less')