24 replies

CSS Z-index changing unexpectedly

I have simplified this just to show what is going on. I have a box (originally a button), with a 3D effect. When it is hovered over, the box rises by 2 pixels and the 3D effect drops by 3 pixels (hiding it). However, for some reason the 3D effect behind the box moves in front. Can anyone explain why this is please? https://codepen.io/iBlackwolf/pen/ZEZWdQx

<!DOCTYPE html>
<html lang="en">

    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">

        <title>Hmmmmmmm</title>
        <style>
            body {
                width: 100vw;
                height: 100vh;
                display: flex;
                flex-direction: column;
                align-items: center;
                justify-content: center;
            }

            #box {
                position: relative;
                width: 150px;
                height: 150px;
                border: none;
                border-radius: 30px;
                background-color: #f00;
                font-size: 20px;
                color: #fff;
                cursor: pointer;
            }

            #box::before {
                position: absolute;
                content: '';
                width: 146px;
                height: 150px;
                left: 2px;
                top: -5px;
                border: none;
                border-radius: 30px;
                background-color: #44f;
                z-index: -1;
            }

            #box:hover {
                transform: translateY(-2px);
            }

            #box:hover::before {
                transform: translateY(3px);
            }
        </style>
    </head>

    <body>
        <div id="box"></div>
    </body>

</html>

<!DOCTYPE html>
<html lang="en">

    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">

        <title>Hmmmmmmm</title>
        <style>
            body {
                width: 100vw;
                height: 100vh;
                display: flex;
                flex-direction: column;
                align-items: center;
                justify-content: center;
            }

            #box {
                position: relative;
                width: 150px;
                height: 150px;
                border: none;
                border-radius: 30px;
                background-color: #f00;
                font-size: 20px;
                color: #fff;
                cursor: pointer;
            }

            #box::before {
                position: absolute;
                content: '';
                width: 146px;
                height: 150px;
                left: 2px;
                top: -5px;
                border: none;
                border-radius: 30px;
                background-color: #44f;
                z-index: -1;
            }

            #box:hover {
                transform: translateY(-2px);
            }

            #box:hover::before {
                transform: translateY(3px);
            }
        </style>
    </head>

    <body>
        <div id="box"></div>
    </body>

</html>

CodePenBlackwolf

Strange Hover

...

CSS Z-index changing unexpectedly

<!DOCTYPE html>
<html lang="en">

    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">

        <title>Hmmmmmmm</title>
        <style>
            body {
                width: 100vw;
                height: 100vh;
                display: flex;
                flex-direction: column;
                align-items: center;
                justify-content: center;
            }

            #box {
                position: relative;
                width: 150px;
                height: 150px;
                border: none;
                border-radius: 30px;
                background-color: #f00;
                font-size: 20px;
                color: #fff;
                cursor: pointer;
            }

            #box::before {
                position: absolute;
                content: '';
                width: 146px;
                height: 150px;
                left: 2px;
                top: -5px;
                border: none;
                border-radius: 30px;
                background-color: #44f;
                z-index: -1;
            }

            #box:hover {
                transform: translateY(-2px);
            }

            #box:hover::before {
                transform: translateY(3px);
            }
        </style>
    </head>

    <body>
        <div id="box"></div>
    </body>

</html>

<!DOCTYPE html>
<html lang="en">

    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">

        <title>Hmmmmmmm</title>
        <style>
            body {
                width: 100vw;
                height: 100vh;
                display: flex;
                flex-direction: column;
                align-items: center;
                justify-content: center;
            }

            #box {
                position: relative;
                width: 150px;
                height: 150px;
                border: none;
                border-radius: 30px;
                background-color: #f00;
                font-size: 20px;
                color: #fff;
                cursor: pointer;
            }

            #box::before {
                position: absolute;
                content: '';
                width: 146px;
                height: 150px;
                left: 2px;
                top: -5px;
                border: none;
                border-radius: 30px;
                background-color: #44f;
                z-index: -1;
            }

            #box:hover {
                transform: translateY(-2px);
            }

            #box:hover::before {
                transform: translateY(3px);
            }
        </style>
    </head>

    <body>
        <div id="box"></div>
    </body>

</html>

CodePenBlackwolf

Strange Hover

...

CSS Z-index changing unexpectedly

CSS Z-index changing unexpectedly

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