header-footer.css

/* HEADER */
header {
  position: -webkit-sticky;
  position: sticky;
  top: 0;
  z-index: 999;
  width: 100%;
  background: #5cdb94;
  color: #17242a;
  font-size: 16px;
  display: flex;
  align-items: stretch;
  justify-content: space-between;
}
header a:focus, 
header a:hover {
  text-decoration: none;
  color: currentColor;
}
header .logo {
  color: inherit;
  text-decoration: none;
  display: block;
  line-height: 2em;
  padding-left: 20px;
  padding-top: 0.5em;
}
header .name {
    font-weight: bold;
    font-size: 1.5em;
}
header .slogan {
  margin-left: 1em;
  padding-left: 1em;
  border-left: 1px solid currentColor;
}
header nav {
  display: flex;
  padding-right: 20px;
}
header nav .item, 
header label {
  text-decoration: none;
  display: block;
  padding: 0.5em 1em;
  line-height: 2em;
  cursor: pointer;
  color: inherit;
  font-weight: normal;
  white-space: nowrap;
}
header label {
  padding: 0.5em 20px;
}
header nav .item.boxed:focus, 
header nav .item.boxed:hover {
  background-color: transparent;
  color: #17242a;
}

@media not all and (max-width: 900px) {
  header nav .item:not(.boxed) {
    box-shadow: inset 0 0 currentColor;
    transition: box-shadow 0.1s;
  }
  header nav .item:not(.boxed):focus, 
  header nav .item:not(.boxed):hover {
    box-shadow: inset 0 -4px #17242a;
  }
  header nav .item.boxed {
    margin: 0 0 0 0.5em;
    padding: 0 calc(1em + 2px);
    background-clip: padding-box;
    background-color: #17242a;
    color: #fff;
    box-shadow: inset 0 0 0 2px #17242a;
    border-radius: 0.8em;
    /* Note IE/Edge mangle this; workaround at EOF */
    border: calc(0.5em + 0.4px) solid #5cdb94;
  }
  header #show-nav, 
  header label {
    display: none;
  }
}

@media (max-width: 1000px) {
  header .slogan {
    display: none;
  }
}

@media (max-width: 900px) {
  header #show-nav:checked ~ .logo {
    z-index: 10;
    padding-top: 13px;
  }
  header #show-nav:checked ~ .logo .slogan {
    display: none;
  }
  header #show-nav:checked ~ label {
    padding: 15px 20px 0.5em 20px;
  }
  header #show-nav {
    display: block;
    position: absolute;
    top: -99em;
    left: -99em;
  }
  header #show-nav ~ label {
    position: relative;
    z-index: 10;
    background: transparent; /* remove background in safari */
  }
  header #show-nav:not(:checked) ~ label::before {
    content: "Menu";
    margin-right: 0.5em;
  }
  header #show-nav ~ label::after {
    content: url("data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20width='15'%20height='11'%3E%3Cpath%20d='M0,.5h15m0,5h-15m0,5h15'%20stroke='%2317242a'/%3E%3C/svg%3E");
  }
  header #show-nav:checked ~ label::after {
    content: url("data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20width='16'%20height='16'%3E%3Cpath%20d='M0,0l16,16m0-16l-16,16'%20stroke='%2317242a'/%3E%3C/svg%3E");
  }
  header #show-nav:not(:checked) ~ nav {
    display: none;
  }
  header nav.collapsible {
    position: fixed;
    overflow: auto;
    z-index: 9;
    flex-direction: column;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: #69b3e7;
    background: linear-gradient(#5cdb94, #3aafa9);
    padding: 60px 0;
    /* 3em is exact, then some vh factor added for prettiness;
     * 40vw - 60px is eyeballed to be 60px at 300px wide & 260 at 800 */
    box-shadow: 0.1em 0.2em 0.3em rgba(51, 62, 72, -0.5);
    text-align: left;
    border-radius: 0 0 0.2em 0.2em;
    animation: 0.2s nav-appear;
  }
  header nav .item {
    padding: 10px 20px;
    margin: 0;
    border-bottom: 1px solid #fff 8;
    box-sizing: border-box;
  }
  header nav .item:not(.boxed):focus, 
  header nav .item:not(.boxed):hover {
    background: #17242a;
    color: #fff;
  }
  header nav .item.boxed {
    margin: 30px 20px 0 20px;
    border: 1px solid #17242a;
    border-radius: 4px;
    text-align: center;
    padding: 5px 0;
    box-sizing: border-box;
    background-color: #17242a;
    color: #fff;
  }
}


@keyframes nav-appear {
    0% {
        opacity: 0;
    }
}

/* IE and Edge≤15 mangle the inner shadow radius; I reported it at
https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/12515080/
and it got fixed for Edge 16. I have no good CSS hack to target Edge≤15, so I’m
just going to ignore it, and only fix it for IE. */
@media not all and (max-width: 900px) {
    _:-ms-input-placeholder, /* this selector targets IE10–11 only */
    body > header > nav .item.boxed {
        /* We *could* make this abandon the border and padding trick, but this
         * time I’m just going to drop the border-radius. More succinct. */
        border-radius: 0;
    }
}

/* FOOTER */
footer {
    position: relative;
    z-index: 999;
    background: #5cdb94;
    text-align: center;
    padding: 15px 0;
}
footer a {
    display: inline-block;
    padding: 0 1em;
    color: #17242a !important;
    text-decoration: none;
}
footer a:focus,
footer a:hover {
    text-decoration: underline;
}

@media (max-width: 600px) {
    footer a {
        padding: 0.5em 1em;
    }
}

/* Footer ribbon 
body::after {
    content: "";
    display: block;
    width: 100%;
    height: 5px;
    background: linear-gradient(90deg, #17242a, #0fe7dc, #17242a);
    position: relative;
    z-index: 1000;
}*/