Give this CSS a shot.
.Skin .SkinInner {
margin: 0 0 0 auto;
}
In case the default styles are winning the cascade battle, you can either append !important
.Skin .SkinInner {
margin: 0 0 0 auto !important;
}
or use a heavier base selector:
.Skin #Wrapper .SkinInner {
margin: 0 0 0 auto;
}

Thanks alot. That worked even with an Logo implemented!
I implemented this:
.Skin .SkinInner {
margin: 0 0 0 auto !important;
}

Hello there, how can I modify this current code so the left margin is decreased. I want the question box to start from left rather than centre. Thank you.

Change the margin to

margin-left: 0 !important;

AhmedA! Thanks for your great help!! I have another Q, what if I want to make the display margin wider? it is now showing things from left but the text/survey box is narrower than what I need. ...

https://www.qualtrics.com/community/discussion/comment/35424#Comment_35424AhmedA! Thanks for your great help!! I have another Q, what if I want to make the display margin wider? it is now showing things from left but the text/survey box is narrower than what I need. ...
How can I decrease the left margine
.Skin .SkinInner {
  margin-left: 0 !important;
   margin-right: 0 0 0 !auto;
}

Go through this article. It explains the box model, it should provide you with answers to most sizing and positioning related questions.