Update demo videos for navigators

Author: satya164

src/css/custom.css

@@ -181,6 +181,7 @@ article video {
   width: 300px;
   height: auto;
   margin: 16px 0;
+  vertical-align: top;
 }
 
 article video:has(+ video) {

static/assets/7.x/bottom-tabs.mp4

@@ -7,7 +7,7 @@ sidebar_label: Bottom Tabs
 A simple tab bar on the bottom of the screen that lets you switch between different routes. Routes are lazily initialized -- their screen components are not mounted until they are first focused.
 
 <video playsInline autoPlay muted loop>
-  <source src="/assets/navigators/tabs/bottom-tabs-demo.mov" />
+  <source src="/assets/7.x/bottom-tabs.mp4" />
 </video>
 
 ## Installation