Magento – Overriding Blank Theme Styles in Magento 2

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How would you go about overriding the navigation styles for a custom theme when inheriting from the blank theme in Magento 2?

I have a theme.css file in my app/design/frontend/<Vendor>/<theme>/web/css folder, but I am aware that Magento 2 uses LESS. I can easily override the styles within my theme.css stylesheet, but I don't want to have to keep using !important.

Also, I am using Bootstrap 3, and I'm assuming that the styles from the blank theme will override any style instructions that match in Bootstrap. What is the best way to approach this?

Best Answer

The 2 ways recommended by Magento to override or extend the styles from a parent theme:

1. Simple way

Extend:

In your theme directory, create a web/css/source sub-directory. (You've already done this part) Create a _extend.less file there.

According to the documentation:

"Extending a theme using _extend.less is the simplest option when you are happy with everything the parent theme has, but want to add more styles."

Override:

Instead of creating the _extend.less file, you create a _theme.less file. In this case you need to copy all variables you need from the parent _theme.less, including those which will not be changed. Then make your changes.

According to the documentation, the drawback is :

"You need to monitor and manually update your files whenever the parent’s _theme.less is updated."

2. Structured way

Extend:

This method lets you organize your code in a better way. Your changes will be structured. Instead of using a single _extend.less file to include all your changes, you create an extend file for each component from the Magento UI library you want to change.

Say you want to extend styles from button and navigation components. In your theme directory create 2 files: _buttons_extend.less and _navigation_extend.less, then add your changes for each component in the corresponding file.

Then you create the _extend.less file adding this code: 

@import '_buttons_extend.less'; 
@import '_navigation_extend.less';

Override:

In your theme, create a copy of the file corresponding to the UI component you want to change (_buttons.less, _navigation.less, etc) This file will override the _buttons.less of the parent theme.

It is important to notice the difference between override and extend.

You can read more on overriding and extending in this documentation or about CSS in Magento 2 in the Frontend Developer's Guide.

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