Fill element with slanted background on hover

Question

I'm trying to create an CSS button hover effect. But I didn't manage to fill the element with a slanted shape.

How the hover effect was planned:

Screenshot 1: How it looks actually.

Screenshot 2: How I want the hover effect to look like with slanted side.

.button_sliding_bg {
  color: #31302B;
  background: #FFF;
  padding: 12px 17px;
  margin: 25px;
  font-family: 'OpenSansBold', sans-serif;
  border: 3px solid #31302B;
  font-size: 14px;
  font-weight: bold;
  letter-spacing: 1px;
  text-transform: uppercase;
  border-radius: 2px;
  display: inline-block;
  text-align: center;
  cursor: pointer;
  box-shadow: inset 0 0 0 0 #31302B;
  -webkit-transition: all ease 0.8s;
  -moz-transition: all ease 0.8s;
  transition: all ease 0.8s;
}
.button_sliding_bg:hover {
  box-shadow: inset 200px 0 0 0 #31302B;
  color: #FFF;
}

<button class="button_sliding_bg">Buttontext</button>

Answer 1

You can use the technique described in this answer : Fill element from center on hover and skew the pseudo element so it fills the button with a slant :

div {
  position: relative;
  display: inline-block;
  padding: 15px 70px;
  border: 5px solid #B17461;
  color: #B17461;
  font-size: 30px;
  font-family: arial;
  transition: color .5s;
  overflow:hidden;
}
div:before {
  content: '';
  position: absolute;
  top: 0; left: 0;
  width: 130%; height: 100%;
  background: #B17461;
  z-index: -1;
  transform-origin:0 0 ;
  transform:translateX(-100%) skewX(-45deg);
  transition: transform .5s;
}
div:hover {
  color: #fff;
}
div:hover:before {
  transform: translateX(0) skewX(-45deg);
}

<div>BUTTON</div>

Don't forget to add vendor prefixes for browser support (see canIuse for more info).

Answer 2

I believe that you are actually looking for the end state to fill the entire element with background color and not leave the gap. You could also do it with linear-gradient background images and transition their background-size and background-position like in the below snippet.

One disadvantage of using linear-gradient over pseudo-elements or transforms is that the browser support is lower but it doesn't need extra pseudo-elements and so can leave them spare for other use.

.button_sliding_bg {
  color: #31302B;
  background: #FFF;
  padding: 12px 17px;
  margin: 25px;
  font-family: 'OpenSansBold', sans-serif;
  border: 3px solid #31302B;
  font-size: 14px;
  font-weight: bold;
  letter-spacing: 1px;
  text-transform: uppercase;
  border-radius: 2px;
  display: inline-block;
  text-align: center;
  cursor: pointer;
  background-image: linear-gradient(135deg, #31302B 50%, transparent 51%);
  background-size: 100px 100px; /* some initial size to get the slanted appearance */
  background-position: -50px -50px; /* negative positioning to hide it initially */
  background-repeat: no-repeat;
  transition: all ease 0.8s;
}
.button_sliding_bg:hover {
  background-size: 200% 200%; /* 200% because gradient is colored only for 50% */
  background-position: 0px 0px; /* bring it fully into view */
  color: #FFF;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/prefixfree/1.0.7/prefixfree.min.js"></script>
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