WHat does this mean?

[levely]

I just did a fresh install of 2.0.9 and everything went well. When I added a new theme, the forum looked like this:

What's causing this? 

[Herman's Mixen]

Looks that your theme has not al its files, re-upload your files /Themes/theme_name/*.* and set proper permissions on /themes/theme_name for example 755 and beneith

dont post more than 1 topic with the same issue thanks ...

[Illori]

or the paths to the css could be wrong... a link to the forum would be useful so we can tell you what needs to be changed rather then guess.

[kat]

Might be worth going to Admin>Configuration>Themes and layout>Theme Settings, scrolling to the bottom of the page and clicking "Attempt to reset all themes.

Might be...

[levely]

Turned out to be a theme which needed to be uploaded through the package manager. Strange, but it's a great theme.

[Herman's Mixen]

just unpack it locally on your pc, create a new theme name on your FTP location under /Themes/your-chosen-name/

upload the contents of the unpacked theme so that the folders are intact like  /Themes/your-chosen-name/CSS  /Themes/your-chosen-name//Scripts etc.....  /Themes/your-chosen-name/*.*

go to themes and layout --> install from directory  "your-chosen-name" it will read the theme-info.xml at this point and you can set it from the main page from now

The package manager will fail on some hosts, in that case you need to do stuff manually