Theme/ThemeHandler.php
public function getCurrentTheme()
    {
        $theme = $this->getDefaultTheme();
        if ( $this->container->get('session')->has('_admin_theme') ) {
            $theme = $this->container->get('session')->get('_admin_theme');
        }
        return $theme;
    }
public function getCurrentTheme()
    {
        $theme = $this->getDefaultTheme();
        if ( $this->container->get('session')->has('_admin_theme') ) {
            $theme = $this->container->get('session')->get('_admin_theme');
        }
        return $theme;
    }
Gets the current theme used

@return Theme