我的CSS中的Z-Index问题

Question

so I am working on creating a new portfolio for myself and I have just hit a little wall with a CSS issue while trying to style my social icons a certain way. The desired effect I am going for can be seen here: My Social Icons Demo . However, if you view my portfolio, here , you can see that I'm not quite getting the same effect (note: my social icons are located in the top and bottom left corners of the page). I can't seem to get the white background behind my social icon images to transition in. I think this may have to do with a z-index error that is possibly conflicting with something else on my portfolio page but as of right now I am stuck.. any ideas?? Would greatly appreciate it! Code below:

HTML

<!-- SOCIAL -->
                    <div class="col-sm-4 text-left">
                        <div class="social-icons">
                            <a href="https://github.com/jlquaccia" target="_blank" class="me-transparent-btn">
                                <img src="./img/icons/github-6-48.png" alt="Github">
                            </a>
                            <a href="https://www.linkedin.com/profile/view?id=227782654&amp;trk=nav_responsive_tab_profile" target="_blank" class="me-transparent-btn">
                                <img src="./img/icons/linkedin-48.png" alt="LinkedIn">
                            </a>
                            <a href="http://instagram.com/jquatchaa" target="_blank" class="me-transparent-btn">
                                <img src="./img/icons/twitter-48.png" alt="Instagram">
                            </a>
                        </div>
                    </div> 

CSS

.hero {
    background-image: url(../img/star_trails_2_large.jpg);
    background-attachment: fixed;
    background-size: cover;
}

.social-icons {
    margin-top: 41px;

    a {
        display: inline-block;
        width: 50px;
        height: 50px;
        border: 1px solid #fff;
        margin: 5px;
        padding: 0;
        position: relative;
        cursor: pointer;

        img {
            -webkit-filter: invert(100%);
            -moz-filter: invert(100%);
            -ms-filter: invert(100%);
            -o-filter: invert(100%);
            filter: invert(100%);
            vertical-align: bottom;
            display: inline-block;
            -webkit-transform: scale(.7);
            -moz-transform: scale(.7);
            -ms-transform: scale(.7);
            -o-transform: scale(.7);
            transform: scale(.7);
            -webkit-transition: all 400ms ease;
            -moz-transition: all 400ms ease;
            -ms-transition: all 400ms ease;
            -o-transition: all 400ms ease;
            transition: all 400ms ease;
        }

        &:hover img {
            -webkit-filter: invert(0%);
            -moz-filter: invert(0%);
            -ms-filter: invert(0%);
            -o-filter: invert(0%);
            filter: invert(0%);
            -webkit-transform: scale(.8);
            -moz-transform: scale(.8);
            -ms-transform: scale(.8);
            -o-transform: scale(.8);
            transform: scale(.8);
        }

        &:after {
            content: '';
            background: #fff;
            position: absolute;
            width: 0;
            height: 103%;
            opacity: .5;
            -webkit-transition: all 0.3s;
            -moz-transition: all 0.3s;
            -ms-transition: all 0.3s;
            -o-transition: all 0.3s;
            transition: all 0.3s;
            left: 50%;
            top: 50%;
            z-index: -1;
            -webkit-transform: translateX(-50%) translateY(-50%);
            -moz-transform: translateX(-50%) translateY(-50%);
            -ms-transform: translateX(-50%) translateY(-50%);
            -o-transform: translateX(-50%) translateY(-50%);
            transform: translateX(-50%) translateY(-50%);
        }

        &:hover:after {
            opacity: 1;
            width: 105%;
        }
    }
}

.no_margin {
    margin: 50px 0;
}

.img-responsive-center {
    display: inline-block;
    padding-top: 75px;
}

.inner {
    padding-bottom: 100px;

    span {
        color: #EF3D33;
    }
}

.text-center {
    h2 {
        color: white;
    }
}

.delay-05s {
    -webkit-animation-delay: 0.5s;
    animation-delay: 0.5s;
}

.delay-1s {
    -webkit-animation-delay: 1s;
    animation-delay: 1s;
}

.delay-3s {
    -webkit-animation-delay: 3s;
    animation-delay: 3s;
}

@media (max-width: 767px) {
    .social {
        display: none;
    }

    .img-responsive-center {
        padding-top: 100px;
    }
}

.down-btn {
    width: 60px;
    height: 60px;
    background-color: $down-btn-bg;
    -webkit-border-radius: 50%;
    -moz-border-radius: 50%;
    -o-border-radius: 50%;
    border-radius: 50%;
    color: #fff;
    font-size: 20px;
    line-height: 60px;
    -webkit-transition: all 0.5s;
    -moz-transition: all 0.5s;
    -o-transition: all 0.5s;
    transition: all 0.5s;

    &:hover,
    &:focus {
        background-color: $down-btn-hover-focus;
        color: #fff;
    }
}

.down-btn-padding {
    padding-bottom: 80px;
}

Answer 1

Add to your div.social-icons position:relative; z-index:1; position:relative; z-index:1; and this should solve your issue.