support very long dropdown menu

Add

.dropdown-menu {
    max-height: 500px;
    overflow-y: auto;
}

We can make a nicer scroll bar too.

[led]

Would amend this to accommodate any egregiously long menu entries.

.dropdown-menu {
    max-height: 500px;
    overflow-y: auto;
    overflow-x: hidden;
}

[brettryan]

Hey @mdo can you define what is a “very long menu”?

I’m visually impaired (tunnel vision and need to zoom window). For me > 10 menu items means I can’t see them all. 10 isn’t uncommon btw.