Embedding the standard UI within your custom UI can, at first, seem like a good idea. However, some additional work, as outlined below, is still required if you want all of the functionality you see in the standard UI pages. For this reason, my personal preference in Lightning Experience is to extend the standard Lightning Page with custom Lightning Components. You can still provide your own editing experiences for certain fields or data and hook into the same client-side record data and notifications via the Lightning Data Service API.

Depending on the custom UI technology you use, there are different options to embed the standard UI page layout. These options also respect object- and field-level security and, as such, minimize the coding you need to do yourself:

• For Lightning Experience, the lightning:lightning-record-form, lightning:lightning-record-edit-form, and lightning:lightning-record-view-form components support both record editing and viewing within custom UIs built using Lightning Components. However, in contrast to the apex:detail component in Visualforce, custom action buttons are not rendered. 
• For Salesforce Classic, the apex:detail tag can be used on a Visualforce page to render most of the look and feel of the standard UI; note that it is not automatically restyled when the page is shown in Lightning Experience. Also, this component is not very granular; for example, you cannot add your own buttons alongside the standard buttons it renders. This means that your page buttons need to be rendered elsewhere on the page, making the UI look inconsistent and confusing. In addition, this component only renders a read-only view of the record layout.