I would like to add a menu left to a div but fixed relative to the top of the body. So when I scroll the div, the left menu sticks to the screen.
You will have to follow some steps:
First of all, you will have to display your menu as
Second, to position it on the top of the
body, you will have to use
top: 0 (or you can change it to your desired top taking as reference the body tag).
As the content div occupy the 70% of the width of the screen with
margin: auto it means that it has 15% (30% that is not occupy and the same at each side, 30%/2 = 15%) of the screen on each side so you will have to use calc to rest to the 15% of each side, the 50px that occupy your menu.
Remove the default margin of your