If you are using Xampp on Windows, you may face to the issue when you install Magento 2.3.0.
You cannot login to Magento backend because the Login form does not appear.
How to fix this issue.
Step 1: Open Validator.php file in vendor\magento\framework\View\Element\Template\File
Step 2: Go to line 138 to change the scripts.
Orginal scripts
$realPath = $this->fileDriver->getRealPath($path);
Change to
$realPath = str_replace('\\', '/', $this->fileDriver->getRealPath($path));
it should be like below screenshot
DONE!!!