I haven’t fully researched on this type but using the 2nd type of my code, some css doesn’t work but trying the 1st one works perfectly. Yeah XHTML 1.0 Transitional, has something to do with that but haven’t fully read on it. Will research more of this 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">