ホバー メニューの背景がスムーズに移行しないのはなぜですか?

#content #nav a:hover {
    color: black;
    background-color: #AD310B;
    -moz-transition: all 1s ease-in;
    -webkit-transition: all 1s ease-in;
    -o-transition: all 1s ease-in;
    transition: all 1s ease-in;
}

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>