Generated by SassMeister.com.

SassMeister-input-HTML.html

<div id="header">Header-Div</div><div id="sidebar">Sidebar-Div</div>

SassMeister-input.scss

// ----
// Sass (v3.4.7)
// Compass (v1.0.1)
// ----

$breite: 500px;

#header { 
  float:left;
  width:$breite;
  height:50px;
  background-color:#000;
  color:#fff;
}
#sidebar {
  width:$breite*0.2;
  height:50px;
  float:left;
  background-color:#675;
  color:#fff;
}

SassMeister-output.css

#header {
  float: left;
  width: 500px;
  height: 50px;
  background-color: #000;
  color: #fff;
}

#sidebar {
  width: 100px;
  height: 50px;
  float: left;
  background-color: #675;
  color: #fff;
}

SassMeister-rendered.html

<div id="header">Header-Div</div><div id="sidebar">Sidebar-Div</div>