It is currently possible to modify the portal's default CSS and add your own styles. To modify the CSS styles you need to access the "site administration", "Settings", "customize Transparency", css tab:

Example path to customize transparency

Add the desired content

Using this CSS change you can:

Change header color and margins:

Change color with HTML codeExample of changed color

Add an image to the header:

Add an image with HTML codeExample of the portal with the image already changed

Change the font style of a site:

Change font style with html codeExample with changed font