1. style.css file for dark version email template

2. style-light file for light version email template

3. When submit email template then add style/style-light.css code copy and embed which file that are integrated as email template. Like: 

    step-1: Open crypto.html file on your editor

    step-2: Open style.css file on your editor

    step-3: Copy style.css file code

    step-4: Paste crypto.html file in head section