display tooltip with link address when hovering over link

This feature was accidentally deleted during the Gmail transition.

app/main/index.js

@@ -1,3 +1,4 @@
+const fs = require('fs');
 const path = require('path');
 const {
   app, BrowserWindow, Menu, shell, ipcMain, nativeImage, Notification, dialog,
@@ -150,6 +151,10 @@ app.on('ready', () => {
 
   const { webContents } = mainWindow;
 
+  webContents.on('dom-ready', () => {
+    webContents.insertCSS(fs.readFileSync(path.join(__dirname, '../renderer/browser.css'), 'utf8'));
+  });
+
   webContents.on('will-navigate', (e, url) => {
     if (config.get('sendAnalytics')) analytics.track('will-navigate');
     if (!allowedUrl(url)) {

app/renderer/browser.css

@@ -0,0 +1,22 @@
+/* Tooltip to display link contents */
+/* <div class="AO"> contains message view area (right side of window) */
+div.AO a[href]::after {
+    content: attr(href);
+    position: absolute;
+    transform: translateY(100%);
+    left: 0;
+    background: rgba(0,0,0,0.7);
+    text-align: center;
+    color: #fff;
+    font-size: small;
+    border-radius: 5px;
+    pointer-events: none;
+    padding: 4px 8px;
+    z-index:99;
+    opacity:0;
+    transition: opacity 0.5s;
+}
+
+div.AO a[href]:hover::after {
+   opacity:1
+}