webview: Update z-index for left-sidebar and webview.

Regression from c11089027c.

app/renderer/css/main.css

@@ -28,6 +28,7 @@ body {
     -webkit-app-region: drag;
     overflow: hidden;
     transition: all 0.5s ease;
+    z-index: 2;
 }
 
 .toggle-sidebar div {
@@ -86,7 +87,6 @@ body {
     flex-direction: column;
     position: fixed;
     bottom: 0;
-    width: inherit;
 }
 
 .action-button {
@@ -249,28 +249,34 @@ body {
 }
 
 webview {
-    opacity: 1;
     /* transition: opacity 0.3s ease-in; */
     flex-grow: 1;
+    position: absolute;
+    width: 100%;
+    height: 100%;
+    flex-grow: 1;
+    display: flex;
+    flex-direction: column;
 }
 
 webview.onload {
     transition: opacity 1s cubic-bezier(0.95, 0.05, 0.795, 0.035);
 }
 
-webview.disabled {
-    flex: 0 1;
-    height: 0;
-    width: 0;
-    opacity: 0;
-    transition: opacity 0.3s ease-out;
+webview.active {
+    opacity: 1;
+    z-index: 1;
+    visibility: visible;
 }
 
-webview:focus {
+webview.disabled {
+    opacity: 0;
+}
+
+webview.focus {
     outline: 0px solid transparent;
 }
 
-
 /* Tooltip styling */
 
 #back-tooltip,
@@ -278,7 +284,7 @@ webview:focus {
 #setting-tooltip {
     font-family: sans-serif;
     background: #222c31;
-    margin-left: 68px;
+    margin-left: 45px;
     padding: 6px 8px;
     position: absolute;
     margin-top: 0px;

app/renderer/js/components/webview.js

@@ -130,6 +130,7 @@ class WebView extends BaseComponent {
 		}
 
 		this.$el.classList.remove('disabled');
+		this.$el.classList.add('active');
 		setTimeout(() => {
 			if (this.props.role === 'server') {
 				this.$el.classList.remove('onload');
@@ -168,6 +169,7 @@ class WebView extends BaseComponent {
 
 	hide() {
 		this.$el.classList.add('disabled');
+		this.$el.classList.remove('active');
 	}
 
 	load() {

package.json

@@ -18,7 +18,7 @@
     "url": "https://github.com/zulip/zulip-electron/issues"
   },
   "engines": {
-    "node": ">=8.0.0"
+    "node": ">=6.0.0"
   },
   "scripts": {
     "start": "electron app --disable-http-cache --no-electron-connect",