I tried overwriting the "margin-bottom: 20px" in .nav by changing the value into "margin-bottom: 0" but it does work. It is only used once for a specific webpage.
I don't know what to do?
I still wanto to keep the original value "margin-bottom: 20px" because it is used in other webpages.
<style>
.nav{
margin-bottom: 20px;
}
</style>
Use inline style which has higher priority and will work since you are using only for a single page.