CSS box-shadow transition

Question

I have several div elements on my website that are part of a class that has an inset box-shadow. When I hover over those div boxes, I want the inset property removed from the box-shadow, and I want it to transition to an outward shadow. However, though the shadow changes correctly, it doesn't transition during the change. It just instantly switches shadows. How do I fix this?

Here's the HTML:

<header>

    <div id="header-stuff">

        <p class="header-big">Green Homes 101</p>

        <div id="header-links">

            <div class="header-link">
                <a href="alt-en.html#top">
                    <img src="images/index/alt-en.svg" alt="Alternate Energy" />
                    <p>Alternate Energy</p>
                </a>
            </div>

            <div class="header-link">
                <a href="diy.html#top">
                    <img src="images/index/diy.svg" alt="DIY" />
                    <p>DIY</p>
                </a>
            </div>

            <div class="header-link">
                <a href="buying.html#top">
                    <img src="images/index/buying.svg" alt="Buying Green Homes" />
                    <p>Buying Green Homes</p>
                </a>
            </div>

            <div class="header-link">
                <a href="about.html#top">
                    <img src="images/index/about.svg" alt="About Us" />
                    <p>About Us</p>
                </a>
            </div>

        </div>

    </div>

</header>

And here's the CSS:

.header-link {
    display: inline-block;
    background-color: rgba(50, 125, 42, 0.75);
    margin: 1%;
    overflow: hidden;
    border-radius: 10%;
    box-shadow:0 0 10px rgba(0, 0, 0, 0.7) inset;

    -ms-transition: all .25s linear;
    -moz-transition: all .25s linear;
    -webkit-transition: all .25s linear;
    -o-transition: all .25s linear;
}

.header-link > a {
    display: block;
    width: 100%;
    height: 100%;
    color: rgba(10, 85, 2, 0.35);
    text-shadow: 1px 4px 6px rgba(33, 108, 25, 0.85), 0 0 0 #000, 1px 4px 6px rgba(33, 108, 25, 0.85);
    border-radius: 10%;
}

.header-link > a > img {
    display: block;
    width: 100%;
    height: 80%;
}

.header-link:hover {
    background-color: #1e9cd7;
    box-shadow:0 0 10px rgba(0, 0, 0, 0.7);

    -ms-transition: all .25s linear;
    -moz-transition: all .25s linear;
    -webkit-transition: all .25s linear;
    -o-transition: all .25s linear;
}

Answer 1

You can not transition from a normal box shadow to a inset box shadow.

Luckily, you can set multiple box shadows, so you can write

.header-link {
    box-shadow:0 0 10px rgba(0, 0, 0, 0.7) inset, 0px 0px 0px white;
}

and

.header-link:hover {
    box-shadow: 0px 0px 0px white inset, 0 0 10px rgba(0, 0, 0, 0.7);
}

Notice that these shadows are the same that the ones that you had, because the extra shadow has 0px, so won't be displayed. Notice also that the order is important: the browser will transition it only if the first shadow is inset (or normal) in both, the second one is inset (or normal) in both, and so on

fiddle

I have removed the transitions in the hover state, you don't need to repeat them.