How to make markdown text specific to mobile sites

How do I make my colours to invert when the mobile site is loaded.

On desktop, it loads with white text on a black background, but I want black text with a white background for mobile.

Also, I would like to get ride of the line break "BOOK your ride, and more" on the mobile site.

Here is my current markdown code:

<div style="background-color:black; text-align:left; vertical-align: middle; padding:20px 0;">
<h1 style="background-color:black;">WE KNOW YOU'RE BUSY.</h1>
</div>

<div style="background-color:black; text-align:left; vertical-align: middle; padding:10px 0; margin-top:10px">
<h4>Access your account, BOOK your ride, and more,<br>while you’re on the go with our <b>mobile app!</b></h4>
</div>

<div class="black">

Can you share link to page where you inserted Markdown? We can check easier.