When I was working in WordPress I came across this serious issue of white border around my Home page. Then I found a great solution to overcome it. And that is why I am sharing it with you.
1. Go to your dashboard by logging in –>Select Appearance –> Editor–> Header.php
2. Add the following code before </head> in your Header.php
3. Upload it and refresh the page . You will find that the white border has been removed.