Custom Checkbox and Radio
Custom Checkboxes

Use Bootstrap's .custom-control classes for Custom Checkboxes.

Custom Checkbox Colors

Add .custom-control-indicator-[variation] to .custom-control-indicator for custom colors.

Add .custom-control-material for flat checkbox

Custom Radio

Use Bootstrap's .custom-control classes for Custom Radio.

Custom Radio Colors

Add .custom-control-indicator-[variation] to .custom-control-indicator for custom colors.

Custom Dropdowns
Custom Select

Add a .custom-select to select for a Custom Dropdown

Custom File Upload
Files

Add a .custom-file to a label for File Input for custom style