XML:
<referenceBlock name="customer_account_navigation">
<block class="Magento\Customer\Block\Account\SortLinkInterface" name="customer-account-navigation-account-link">
<arguments>
<argument name="label" xsi:type="string" translate="true">Account Dashboard</argument>
<argument name="path" xsi:type="string">customer/account</argument>
<argument name="sortOrder" xsi:type="number">250</argument>
<argument name="css_class" xsi:type="string">my-custom-css-class-here-not-working</argument>
</arguments>
</block>
<!-- @Prashant Valanda suggestion -->
<referenceBlock name="customer-account-navigation-account-link">
<arguments>
<argument name="label" xsi:type="string" translate="true">Account Dashboard works</argument>
<argument name="path" xsi:type="string">customer/account</argument>
<argument name="sortOrder" xsi:type="number">250</argument>
<argument name="css_class" xsi:type="string">but-my-custom-css-class-here-still-does-not-work</argument>
</arguments>
</referenceBlock>
</referenceBlock>
Taken from /../vendor/magento/module-customer/view/frontend/layout/customer_account.xml
Any ideas how one can add css class?