How to format a book’s index in order to make delimiting letters bold?

I have an index. It looks good. I really want to make the letters that start a particular series of indexes (car, crane, crumple, etc.) bold and add some space right above it in order to make it look better.

How can I do that?

What I do in this case is to request from the index generator that it adds an “alphabetical delimiter” when there is a break in alphabetic ordering. If your index is already generated, right-click on it and choose Edit Index. Other, Insert>Table of Contents & Index>Table of Contents, Index or Bibliography where you want to insert your index.

Go to Entries tab and check Alphabetical delimiter. This will generate initials before a block of terms beginning with the same character (not necessarily a letter).

The appearance of the index delimiter is controlled by paragraph style Index Separator. Modify this style to fit your needs (spacing, font, weight, colour, …).

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If you do not use the automatic Alphabetical delimiter but use your own keys, then you should look at tab Styles in the Edit Index dialog. It lists, which paragraph styles are associated to the lines of the index. You can reassign it there and you can edit the paragraph style from there. Only a new paragraph style need to be defined before. In the paragraph style you can set e.g. a distance above. In case Alphabetical delimiter is not used, the keys are on level 1 and the index terms on level 2.

To format a special part of an index line, click on that part in the Entries tab of the dialog. Then you can select the Character style for that part.

The character style Main Index Entry does not belong to the entry text, but to the page number. If you mark an index entry as Main entry, then for this item the character style Main Index Entry is used for the page number.

Once I figured out how to edit the index, the rest was easy. Thank you!!