core-bundle/src/Resources/contao/classes/Backend.php
public static function getThemes()
	{
		$arrReturn = array();
		$rootDir = System::getContainer()->getParameter('kernel.project_dir');
		$arrThemes = scan($rootDir . '/system/themes');

		foreach ($arrThemes as $strTheme)
		{
			if (strncmp($strTheme, '.', 1) === 0 || !is_dir($rootDir . '/system/themes/' . $strTheme))
			{
				continue;
			}

			$arrReturn[$strTheme] = $strTheme;
		}

		return $arrReturn;
	}
public static function getThemes()
	{
		$arrReturn = array();
		$rootDir = System::getContainer()->getParameter('kernel.project_dir');
		$arrThemes = scan($rootDir . '/system/themes');

		foreach ($arrThemes as $strTheme)
		{
			if (strncmp($strTheme, '.', 1) === 0 || !is_dir($rootDir . '/system/themes/' . $strTheme))
			{
				continue;
			}

			$arrReturn[$strTheme] = $strTheme;
		}

		return $arrReturn;
	}
Return the back end themes as array

@return array An array of available back end themes