XF 2.3 What's this line doing? width: calc(100% - 36px)

[securedme]

.node-body .node-main {width: calc(100% - 36px); padding-right:0px;}

It appears in my extra.less but I have no idea what exactly is its purpose.

 

[digitalpoint]

It's giving you a width that's 36px less than 100%. So if the browser window was 1000px wide, it would be 964px. If it was 500px wide, it would be 464px.