ThemeProvider (#677)

closes #655

app/components/Sidebar/components/Header.js

@@ -1,13 +1,12 @@
 // @flow
 import Flex from 'shared/components/Flex';
 import styled from 'styled-components';
-import { color, fontWeight } from 'shared/styles/constants';
 
 const Header = styled(Flex)`
   font-size: 11px;
-  font-weight: ${fontWeight.semiBold};
+  font-weight: 600;
   text-transform: uppercase;
-  color: ${color.slateDark};
+  color: ${props => props.theme.slateDark};
   letter-spacing: 0.04em;
   margin-bottom: 4px;
 `;