Custom Theme – Fix styles-m.css Failed to Open Stream Error

SOLUTION # 1 (IF YOU WANT TO EDIT XML FILE)

I would like you to download Magento 2 zip from magentocommerce.com/download with sample data, create new db in phpmyadmin, extract zip in htdocs folder. Install Magento 2 but do not use localhost use 127.0.0.1 in store URL and admin URL. After successful installation DO NOT run magento.

Now we are going to clear / delete caches and sessions of Magento 2. Go to following paths and delete everything:

ROOT > var > cache > *DELETE ALL*
ROOT > var > page_cache > *DELETE ALL*
ROOT > var > session > *DELETE ALL*

When Magento 2 is not in production mode, it will try to create symlinks for some static resources on local server. We have to change that behavior of Magento 2 by going to edit ROOT > app > etc > di.xml file. Open up di.xml in your favorite code editor, find the virtualType name="developerMaterialization" section. In that section below, you will find an item <item name="view_preprocessed" xsi:type="object"> which needs to be modified. You can modify it by changing the following content:

Magento\Framework\App\View\Asset\MaterializationStrategy\Symlink

To:

Magento\Framework\App\View\Asset\MaterializationStrategy\Copy

Now last step, also delete old files generated in ROOT > pub > static > DELETE ALL EXCEPT .HTACCESS

SOLUTION # 2

Install Composer. Now I would like you to download Magento 2 zip from magentocommerce.com/download, create new db in phpmyadmin, extract zip in htdocs folder. Install Magento 2 but do not use localhost use 127.0.0.1 in store URL and admin URL. After successful installation DO NOT run magento.

Now we are going to verify Composer installation, Deploy static content, clear / flush Magento cache and reindex the Magento 2 blocks. To perform all above actions, press WINDOWS KEY + R to open RUN dialog and type “cmd” to open Command Prompt.

Type “cd PATH_TO_YOUR_MAGENTO2_FILES” to enter in Magento 2 ROOT directory.

Now to verify Composer installation in above directory, type “composer install”.

If you get any error in this step, please check your Composer installation

In this step, we are setting up static content to deploy on our Magento store. To perform this, type “php bin/magento setup:static-content:deploy”.

For Those who are on Magento 2.2.x

php bin/magento setup:static-content:deploy -f

If you get any error, check your PHP.EXE and PHP.INI Environment Variable

Clear / Flush Magento cache by typing “php bin/magento cache:flush” in CMD.

And finally, to Reindex Magento Static Blocks type “php bin/magento indexer:reindex”.

You are done with successful installation of Magento 2.

Seem that your custom css put wrong place, it should be under web/css folder in your custom theme : app/design/frontend/vendor/theme/web/css/local-l.css.

Remember to run static content deploy again.