Override frontend_default.css

-- HikaShop version -- : 6.1.1
-- Joomla version -- : 5.4.0
-- PHP version -- : 8.3
-- Browser(s) name and version -- : Firefox

How can i make an override for frontend_default.css?

Setting overrides in my custom.css file doesn't work. The Cart Buttons are green in Pop-up. I need it #ef7d00;

.hikacart {
color: #fff;
background-color: #ef7d00;
border-color: #ef7d00;
}
.hikacart:focus {
color: #fff;
background-color: #ef7d00;
border-color: #ef7d00;
}
.hikacart:hover {
color: #fff;
background-color: #ef7d00;
border-color: #ef7d00;
}