.header {
    background: inherit;
    background-image: 
      linear-gradient(
        rgba(0, 0, 0, 0.15),
        rgba(0, 0, 0, 0.15)
      ),
      url(../images/header-background-1920px.jpg);     
    background-repeat: no-repeat;
    background-position: center center;
    background-size: cover;
    background-attachment: fixed;  
}

a#connect-strava {
    border-radius: 0.375rem;
}
a#connect-strava img {
    max-width: 100%;
    width: 224px;
    border-radius: 0.375rem;
}
span#connected-to-strava,
a#link-to-prefs{
    display: inline-block;
    width: 217px;
    height: 49px;
    border-radius: 0.375rem;
    color: white;
    background-color: grey;
    text-transform: none;
    font-weight: bold;
    padding-top: 14px;
}
.about-detail, .section-item-detail, .contact p {
    color: #000;
    font-size: 15px;
}

p.about-detail {
    margin: 0 0 20px;
}

.credits {
    background: #f3f3f3;
}
.credits p {
    text-align: center;
    font-weight: bold;
    font-size: 18px;
}

.bg-danger {
    color: black;
    padding: 15px;
}

@media (max-width: 960px){
    .header {
        background-image: 
            linear-gradient(
                rgba(0, 0, 0, 0.15),
                rgba(0, 0, 0, 0.15)
            ),
            url(../images/header-background-portrait-860px.jpg);
    }
}

@media (max-width: 480px){
    .header {
            linear-gradient(
                rgba(0, 0, 0, 0.15),
                rgba(0, 0, 0, 0.15)
            ),
            url(../images/header-background-portrait-430px.jpg);
    }
}