Bootstrap: Change dropdown item background on hover

When trying to override the background color of a hovered submenu in Bootstrap you may be surprised to find that simply setting background-color on the element doesn’t suffice.

Bootstrap defines a background image for the elements to overcome some clashes in their media queries.
To set a solid background color, remove the image and set a color as usual:

.dropdown-menu > li > a:hover {
    background-image: none;
    background-color: red;