Sometimes a custom module isn't enough - you want to specifically adjust an existing Hyvä or Magento default template, without touching the core. That's what Magento's theme fallback mechanism is for, and it applies unchanged in Hyvä projects too.

How the fallback works

Magento looks for a template in this order, until it finds one:

1. in the active theme, in the matching module subfolder (app/design/frontend/Mironsoft/default/[Module]/templates/...)
2. in the active theme's parent theme (i.e. in the Hyvä CSP theme itself)
3. in the module that originally defines the template (app/code/.../view/frontend/templates/...)

If a template is placed in the child theme under the exact same relative path as in the module or parent theme, the child theme version wins automatically - without configuring "override" explicitly anywhere.

Example: adjusting the mini cart

Say Hyvä's default mini cart template lives (simplified) at Magento_Checkout/templates/cart/minicart.phtml in the parent theme. To customize it, you create the exact same relative path structure in your own child theme:

app/design/frontend/Mironsoft/default/
└── Magento_Checkout/
    └── templates/
        └── cart/
            └── minicart.phtml   ← overrides the Hyvä version

The module folder name (Magento_Checkout) and the path after it must match exactly - even a small typo means Magento keeps using the original template, without reporting an error.

Alternative: referenceBlock instead of a full copy

Not every adjustment needs a full template copy. If you only want to change one argument or remove a block, a <referenceBlock> in the Layout XML (see chapter 6) is often enough - without touching the actual PHP template file at all. That's the lower-maintenance solution and should be preferred wherever possible.