Responsive Skewed Panels With Pure CSS / CSS3

Responsive, fullscreen, skewed panels with an expanding effect on mouse hover. Heavily based on CSS3 flexbox model.

How to use it:

Build the html structure for the skewed panels.

<main>
  <section>
    <article>
      Panel 1
    </article>
  </section>
  <section>
    <article>
      Panel 2
    </article>
  </section>
  <section>
    <article>
      Panel 3
    </article>
  </section>
  <section>
    <article>
      Panel 4
    </article>
  </section>
  <section>
    <article>
      Panel 5
    </article>
  </section>
</main>

The main CSS / CSS3 styles.

main {
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-orient: vertical;
  -webkit-box-direction: normal;
  -webkit-flex-direction: column;
  -ms-flex-direction: column;
  flex-direction: column;
  width: 100%;
  -webkit-transform: translate3d(0, 0, 0);
  transform: translate3d(0, 0, 0);
}
@media (min-width: 630px) {
main {
  -webkit-box-orient: horizontal;
  -webkit-box-direction: normal;
  -webkit-flex-direction: row;
  -ms-flex-direction: row;
  flex-direction: row;
  width: 130%;
  margin-left: -15%;
}
}
main section:not(:first-child):not(:last-child):hover {
  -webkit-box-flex: 2;
  -webkit-flex: 2;
  -ms-flex: 2;
  flex: 2;
}
main section:not(:first-child):not(:last-child):hover:after { opacity: .8; }
main section:not(:first-child):not(:last-child):hover article {
  opacity: 1;
  -webkit-transform: translateY(0);
  transform: translateY(0);
  -webkit-transition: opacity .2s .2s, -webkit-transform .2s .2s;
  transition: opacity .2s .2s, -webkit-transform .2s .2s;
  transition: opacity .2s .2s, transform .2s .2s;
  transition: opacity .2s .2s, transform .2s .2s, -webkit-transform .2s .2s;
}
@media (min-width: 630px) {
main section:not(:first-child):not(:last-child):hover article {
  -webkit-transform: translateY(0) skewX(-15deg);
  transform: translateY(0) skewX(-15deg);
}
}
section {
  -webkit-box-flex: 1;
  -webkit-flex: 1;
  -ms-flex: 1;
  flex: 1;
  position: relative;
  width: 100%;
  min-height: 20vh;
  overflow: hidden;
  z-index: 1;
  -webkit-transition: flex-grow .2s, opacity .2s, -webkit-box-flex .2s, -webkit-flex-grow .2s;
  transition: flex-grow .2s, opacity .2s, -webkit-box-flex .2s, -webkit-flex-grow .2s;
  transition: flex-grow .2s, opacity .2s;
  transition: flex-grow .2s, opacity .2s, -webkit-box-flex .2s, -webkit-flex-grow .2s, -ms-flex-positive .2s;
}
section:before {
  content: "";
  position: absolute;
  width: 100%;
  height: 100%;
  background-position: center;
  background-size: cover;
  -webkit-transition: width .2s, -webkit-transform .2s;
  transition: width .2s, -webkit-transform .2s;
  transition: transform .2s, width .2s;
  transition: transform .2s, width .2s, -webkit-transform .2s;
}
section:after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: black;
  opacity: 0;
  -webkit-transition: opacity .2s;
  transition: opacity .2s;
}
@media (min-width: 630px) {
section {
  width: 20%;
  height: 100vh;
  margin-right: -1px;
  -webkit-transform: skewX(15deg) translateZ(0);
  transform: skewX(15deg) translateZ(0);
}
section:before {
  left: -100%;
  width: 400%;
  -webkit-transform: skewX(-15deg);
  transform: skewX(-15deg);
}
}

Style the child elements in the CSS as follows:

section:nth-child(1):before {
  background-color: #e60000;
  background-image: url(1.jpg);
}
section:first-child:before, section:last-child:before { background-color: #660000; }
section:first-child:after, section:last-child:after { opacity: .5; }
section:first-child article, section:last-child article { display: none; }
section:nth-child(2):before {
  background-color: #cc0000;
  background-image: url(2.jpg);
}
section:first-child:before, section:last-child:before { background-color: #660000; }
section:first-child:after, section:last-child:after { opacity: .5; }
section:first-child article, section:last-child article { display: none; }
section:nth-child(3):before {
  background-color: #b30000;
  background-image: url(3.jpg);
}
section:first-child:before, section:last-child:before { background-color: #660000; }
section:first-child:after, section:last-child:after { opacity: .5; }
section:first-child article, section:last-child article { display: none; }
section:nth-child(4):before {
  background-color: #990000;
  background-image: url(4.jpg);
}
section:first-child:before, section:last-child:before { background-color: #660000; }
section:first-child:after, section:last-child:after { opacity: .5; }
section:first-child article, section:last-child article { display: none; }
section:nth-child(5):before {
  background-color: maroon;
  background-image: url(5.jpg);
}
section:first-child:before, section:last-child:before { background-color: #660000; }
section:first-child:after, section:last-child:after { opacity: .5; }
section:first-child article, section:last-child article { display: none; }
article {
  position: relative;
  padding: 24px;
  width: 100%;
  height: 100%;
  text-align: center;
  color: white;
  z-index: 1;
  -webkit-transition: opacity .2s, -webkit-transform .2s;
  transition: opacity .2s, -webkit-transform .2s;
  transition: opacity .2s, transform .2s;
  transition: opacity .2s, transform .2s, -webkit-transform .2s;
}
@media (min-width: 630px) {
article {
  display: -webkit-box;
  display: -webkit-flex;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-orient: vertical;
  -webkit-box-direction: normal;
  -webkit-flex-direction: column;
  -ms-flex-direction: column;
  flex-direction: column;
  -webkit-box-align: center;
  -webkit-align-items: center;
  -ms-flex-align: center;
  align-items: center;
  -webkit-box-pack: center;
  -webkit-justify-content: center;
  -ms-flex-pack: center;
  justify-content: center;
  position: absolute;
  top: 0;
  right: 0;
  left: 0;
  margin: auto;
  opacity: 0;
  -webkit-transform: translateY(24px) skewX(-15deg);
  transform: translateY(24px) skewX(-15deg);
}
}
h2 {
  font-size: 32px;
  margin-bottom: 12px;
}