Side Nav Size

Hello, I am planning on creating my own custom UI/UX by using webflow and using it through Iframe as a side nav. However I am not finding any way to reduce the bulky size of the nav bar. I would love to extend my main content section to take up more space since I will have simple icons the size of the bubbles on top navigator.

Also on a side note, I would love the ability to choose a light mode iframe and one for dark mode. So I can get the colors right. Lastly, even though I have the same rgb color of the bettermode site there is still a while line all around the iframe. Any way to remove that?

Here is an example on how out of place this looks:

Here is what I am hoping to accomplish