MediaWiki:Common.css

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/* CSS placed here will be applied to all skins */
/* Categories (single star) - Make them bold and slightly larger */
#mw-panel .portal ul > li {
    font-weight: bold;
    font-size: 110%; /* Slightly larger font size than subcategories */
    color: #000000; /* Default color (black), change if needed */
}

/* Subcategories (double star) - Keep normal size */
#mw-panel .portal ul ul li {
    font-weight: normal;
    font-size: 100%; /* Normal font size */
    color: #333333; /* Subcategories color (dark gray), adjust if needed */
}