The macron (bar above a vowel) is a diacritic that is used to indicate vowel length and stress in Hawaiian and other Polynesian languages.
I asked in this forum about adding a macron, and never got a method my luddite brain could comprehend, but one day I found the characters in Wiki.
Ā using &# plus number 256;
ā 257
Ē 274
ē 275
Ī 298
ī 299
Ō 332
é 333
Ū 362
ū 363

Wiki has characters for macron use with other languages in the same entry. MACRON