see: https://joomla51.com/tutorials/template-customization/adding-new-google-fonts

Tks for reply

I want font like Main Menu from Stella template that show in demo, I think that is "Raleway Thin"
https://www.joomla51.com/demo/0163/

I add insert
../elements/googlefonts.php
$googleFonts['Raleway+Thin'] = 'Raleway Thin';

after changed in admin area , but after save maintain default font

try: $googleFonts['Raleway:wght@100'] = 'Raleway Thin';

stay the same like Raleway font, not Raleway Thin

I try too
$googleFonts['Raleway+Thin:wght@100'] = 'Raleway Thin';

stay like Raleway

Stella menu uses Raleway as font, not thin
try adding this to custom css

.hornav {
font-weight: 100;
}

still the same. tks anyway