You can't.
Mint and Ubuntu, no matter how closely related they are (or aren't, as the case might be) are still two different operating systems.
This is a bad idea.
First, you're mixing two different distributions' packages together. For various reasons, this is a bad idea:
Security.
Stability.
Conflicting updates.
If you let updates go through, you encounter the first two problems, and then you're in deep trouble if say, as an example a kernel update comes through!
Also, this makes getting an accurate bug report or stacktrace almost impossible, if not entirely impossible.
Go to System settings -> Application appearance (or Workspace appearance).
In some items (Colors, Icons, etc) you have the option to:
- Get new (you can search in a dialog box)
- Import (search a downloaded file and install it)
In other items (Style):
- If it's in the repositories: use synaptics (or similar)
- If it isn't in ther repositories: see if there's a PPA and use it
There are other situations that involve compiling a theme, but that's a longer story.
Best Answer
Window decorations
The appearance of window borders, titlebars and buttons.
You will need an engine and a theme.
KDE Style
The elements of a graphical user interface, such as buttons, scrollbars, tabs, and menus.
You will need an engine and a theme.
In this case - QtCurve,Emerald
The QtCurve is in the official Ubuntu repositories. The QtCurve engine can be installed with the package: qtcurve
The Smaragd (Emerald for KDE): http://kde-look.org/content/show.php/?content=125162
The Smaragd can be found from the PPA repositories: https://launchpad.net/ubuntu/+ppas?name_filter=smaragd
Download the deb and install it.
Ice cream Theme
Download - unpack the tar package.
Extract the Ice cream QtCurve.emerald to the $HOME/.emerald/theme.
KDE System Settings > Workspace Appearance > Window Decorations > Smaragd
KDE System Settings > Application Appearance > Style > Widget style: QtCurve -> Configure -> Import QtCurve Settings File