How to Remove border-radius on

Using SLDS's input component documentation, you can easily create your custom input box for lightning border:

   Input Label      

 versus using a lightning:input component, which in the end, renders to:

    lightning:input             

Upside of using SLDS custom component: granular control over styling access to DOM (not in lightning namespace) can use custom attributes Upside of using lightning:component includes SLDS styling many build in functionalities Downside of trying to customize a built in component (such as lightning input). Custom CSS may break if changes are made to the component in future releases. Hope this helps you make a choice between applying custom CSS rules to your lightning:input component vs using SLDS with HTML.