Sidebar Full Height

Hello, I need some help with the sidebar of the Twenty Fifteen Theme. I really love the simplexity of this theme.

I change the sidebar to the right which is working but also, I need it to be the full height of the screen. This is the CSS I used to move it to the right.
.sidebar {
float: right;
margin-right: 0px;
max-width: 413px;
position: relative !important;
width: 23%;
background-color: #fff;
}

In order for it to go the full height I need to add the following CSS.
height: 100vh;
top: 0;
bottom: 0;
But in order for those CSS codes to work, I need to change the position from relative to fixed. However, when I do that the sidebar reverts back to the left and then is hidden behind the site content. This is where I am stuck and can’t figure out what I am doing wrong. So your help is much appreciated.