Locator/FileLocator.php
protected function locateAppResource($name, $dir = null, $first = true)
    {
        /** @var AbstractKernel $kernel */
        $kernel = $this->kernel;
        if ($this->kernel instanceof AbstractKernel) {
            $themeName = $this->activeTheme->getName();
            if (isset($kernel->getThemes()[$themeName])) {
                $theme           = $kernel->getThemes()[$themeName];
                $this->lastTheme = $theme->getShortName();
            }
        }

        return parent::locateAppResource($name, $dir, $first);
    }
protected function locateAppResource($name, $dir = null, $first = true)
    {
        /** @var AbstractKernel $kernel */
        $kernel = $this->kernel;
        if ($this->kernel instanceof AbstractKernel) {
            $themeName = $this->activeTheme->getName();
            if (isset($kernel->getThemes()[$themeName])) {
                $theme           = $kernel->getThemes()[$themeName];
                $this->lastTheme = $theme->getShortName();
            }
        }

        return parent::locateAppResource($name, $dir, $first);
    }
Locate Resource Theme aware. Only working for app/Resources.

@param string $name
@param string $dir
@param bool   $first

@return string|array