Hey @pharnos
For the navigation on the left side, this is achieved using New-UDSideNav with the -Fixed switch
Then I modify the look/feel by updating my themes file to include some sidenav customizations
'.sidenav' = @{
'background-color' = "#201F1F"
'margin-top' = "66px"
'height' = "90%"
'width' = "88px !important"
'border-radius' = "0px"
'box-shadow' = "none"
'z-index' = "0"
}
From the CSS above, using the width will shorten your sidenav, also make sure you use !important in some of your styles, as the UD theme will overwrite your customization without this.
As a newcomer to UD, I would recommend your browser developer tools to become your new best friend. This will help you identify what you want/can customize, you can also update the css live in the browser so you know what your end result will look like. once you have the customizations in the browser, copy/paste into your UD theme.
As you can see below, I updated the color of the sidenav to red using developer tools to see your customization/updates in realtime.
UD is soooo customizable, and I find I can quickly enter a rabbit hole with it. My theme.ps1 file is now over 1000 lines 
