Can't make custom.css do its job

Hi there
Get Grav a couple of days
working with win10 , xampp server

I ve create some pages with a quark theme child : mytheme
I hardcoded into the base.html.twig to add my tittle and logo.html.twig to replace the grav logo.
But then i tried to put some personal css into mytheme/css/custom.css nothing happens :-(

Any idea ?

Did you add your custom.css like this:
Add:
{% do assets.addCss('theme://css/custom.css', 98) %}
To (depending on your theme name):
templates/partials/base.html.twig
You might have to add it to head or header.html.twig
As seen here under step 5:
https://learn.getgrav.org/themes/theme-tutorial

add it after style.css.

For more on overriding plugin css: /forum/general/override-plugin-css-t9132