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In that case you can use media query to lower your menu item font size for that device sizes.
Here is a sample code you need to put in your custom CSS:
@media (max-width: 1199px){
.sp-megamenu-parent>li>a, .sp-megamenu-parent>li>span {
font-size: 12px;
}
}
You can use your desired max-width value and set different font size value according to your need.
Note: Path towards custom CSS(Joomla 3): Extensions>Templates>Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.
Note: Path towards custom CSS(Joomla 4): System > Site Templates Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.
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