CSS3 - setting a div to be the viewports' height minus a specific pixel height (within LESS)
// Important point is the tilde. LESS processing of the value without this, will set the output CSS to "height:10vh (as it's assumed that you meant "100vh - 90vh").
// "vh" is just "Viewport Height". It doesn't require cascading "height:100%" declarations.
height:calc(~"100vh - 90px");