Transition of background-color

I'm trying to make a transition effect with background-color when hovering menu items, but it does not work. Here is my CSS code:

#content #nav a:hover {
	color: black;
	background-color: #AD310B;
	/* Firefox */
	-moz-transition: all 1s ease-in;
	/* WebKit */
	-webkit-transition: all 1s ease-in;
	/* Opera */
	-o-transition: all 1s ease-in;
	/* Standard */
	transition: all 1s ease-in;
}

The #nav div is a menu ul list of items.

As far as I know, transitions currently work in Safari, Chrome, Firefox, Opera and Internet Explorer 10+.

This should produce a fade effect for you in these browsers:

a {
    background-color: #FF0;
}

a:hover {
    background-color: #AD310B;
    -webkit-transition: background-color 1000ms linear;
    -ms-transition: background-color 1000ms linear;
    transition: background-color 1000ms linear;
}

<a>Navigation Link</a>

Note: As pointed out by Gerald in the comments, if you put the transition on the a, instead of on a:hover it will fade back to the original color when your mouse moves away from the link.

This might come in handy, too: CSS Fundamentals: CSS 3 Transitions

To me, it is better to put the transition codes with the original/minimum selectors than with the :hover or any other additional selectors:

#content #nav a {
    background-color: #FF0;
    
    -webkit-transition: background-color 1000ms linear;
    -moz-transition: background-color 1000ms linear;
    -o-transition: background-color 1000ms linear;
    -ms-transition: background-color 1000ms linear;
    transition: background-color 1000ms linear;
}

#content #nav a:hover {
    background-color: #AD310B;
}

<div id="content">
    <div id="nav">
        <a href="#link1">Link 1</a>
    </div>
</div>

Another way of accomplishing this is using animation which provides more control.

/* declaring the states of the animation to transition through */
/* optionally add other properties that will change here, or new states (50% etc) */
@keyframes onHoverAnimation {
    0% {
        background-color: #FF0;  
    }
    100% {
        background-color: #AD310B;
    }
}

#content #nav a {
    background-color: #FF0;
    
    /* only animation-duration here is required, rest are optional (also animation-name but it will be set on hover)*/
    animation-duration: 1s; /* same as transition duration */
    animation-timing-function: linear; /* kind of same as transition timing */
    animation-delay: 0ms; /* same as transition delay */
    animation-iteration-count: 1; /* set to 2 to make it run twice, or Infinite to run forever!*/
    animation-direction: normal; /* can be set to "alternate" to run animation, then run it backwards.*/
    animation-fill-mode: none; /* can be used to retain keyframe styling after animation, with "forwards" */
    animation-play-state: running; /* can be set dynamically to pause mid animation*/
    
    
}

#content #nav a:hover {
    /* animation wont run unless the element is given the name of the animation. This is set on hover */
    animation-name: onHoverAnimation;
}