Oh, sorry. That's my misreading and I understood about custom margins with GDoc.Then I tried using landscape-GDoc with all custom margins to 0s, but it did not work for me. (Still having portrait margins)Anyway, thanks again @Joseph_Seddik for your h...

Great!!Thank you @Joseph_Seddik .This method(GDoc to HTML) solved my landscape problem.Additionally I just removed 'max-width' from exported HTML.