Creating a Child Theme

For persistent customizations, create a child theme rather than editing theme files directly. This way your changes survive theme updates.

Create the child theme

Create a folder beside the theme — wp-content/themes/doku-child/ — containing a single style.css:

/*
Theme Name: Doku Child
Template: doku
Version: 1.0.0
*/

/* Your overrides below */
:root {
    --color-accent: #0066cc;
    /* Painted as a background behind existing text, so keep it a
       translucent tint rather than a solid color. */
    --color-accent-hover: rgba(0, 102, 204, .08);
}

Then activate Doku Child under Appearance > Themes.

Why no functions.php or @import

You do not need a functions.php, and you do not need an @import. Doku loads the parent stylesheets itself and then enqueues your child style.css after them, so your overrides win the cascade automatically.

Note: @import is worth avoiding here even though it looks convenient — the browser cannot start fetching the imported file until it has parsed the importing one, so it serializes two downloads that would otherwise run in parallel.

Overriding a rule

To override a rule rather than a variable, write it as you would in any stylesheet — no !important is needed, because the child file loads last:

.doku-sidebar-nav .sidebar-link { font-size: 14px; }