To ensure stability and secure your customizations from being deleted during upgrade, do not change out-of-the-box Magento module and theme layouts. To customize layout, create extending and overriding layout files in your custom theme.
Rather than copy extensive page layout or page configuration code and then modify what you want to change, in the Magento system, you only need to create an extending layout file that contains the changes you want.
For a Magento 2 particular page, its layout is defined by two major layout components: page layout file and page configuration file.
Changing layout files is one of the two possible ways to customize page layout in Magento 2 (the second way is altering templates). To change the page wireframe, modify the page layout files; all other customizations are performed in the page configuration or generic layout files.
Magento 2 application implements the Model-view-controller architecture pattern; meaning, the Magento 2 software is architected into layers, including the view layer.
When you create a Magento 2 theme, you might need to create override files for default theme and module view files. To do so, you must determine which template, layout, and style files Magento uses. This topic describes how to do this.
Magento 2 theme inheritance enables you to easily extend themes and minimize the maintenance efforts. You can use an existing theme as a basis for customizations, or minor store design updates, like holidays decoration. Rather than copy extensive theme files and modify what you want to change, you can add overriding and extending files.
The properties of product images used on the Magento 2 storefront are stored in the view.xml configuration file. This topic provides all details about what properties are available and how to configure them.
After you add your Magento 2 theme to the file system, you can apply it to your store. You apply a theme in Admin.
For the sake of compatibility, upgradability, and easy maintenance, do not modify the out of the box Magento 2 themes. To customize the design of your Magento 2 store, create a new custom theme. This article will show you how to create a Magento 2 theme step by step.