Generated by SassMeister.com.

SassMeister-input-HTML.html

<nav id="tabs">
  <div class="tab active">
    <span>Tab 1</span>
  </div>
  <div class="tab">
    <span>Tab 2</span>
  </div>
</nav>
<div id="page">
  Lorem Ipsum dolor sit amet ...
</div>

SassMeister-input.scss

// ----
// Sass (v3.4.20)
// Compass (v1.0.3)
// ----

body {
  background-color: #000;
  margin: 0;
  padding: 0;
  font-family: sans-serif;
  font-size: 16px;
}

.tab {
  height: 50px;
  width: 150px;
  //border-radius: 15px 15px 0px 0px;
  background-color: #FFF;
  position: relative;
  top: 10px;
  left: 30px;
  display: inline-block;
  z-index: 2;
  //margin-left:5px;
  &.active{
    &:before {
      background-color: white;
    }
    &:after {
      background-color: white;
    }
  }
  &:before {
    height: 50px;
    width: 30px;
    //border-radius: 10px 10px 0px 0px;
    content: "";
    position: absolute;
    left: -15px;
    top: 0px;
    -webkit-transform: skewX(-30deg);
    transform: skewX(-30deg);
    z-index: -1;
  }
  &:after {
    height: 50px;
    width: 30px;
    //border-radius: 10px 10px 0px 0px;
    content: "";
    position: absolute;
    left: 135px;
    top: 0px;
    -webkit-transform: skewX(-30deg);
    transform: skewX(-30deg);
    z-index: -1;
  }
  &:nth-of-type(2) {
    background-color: #555;
    top: 10px;
    left: 56px;
    z-index: 1;
    color: #EEE;
    &:before {
      background-color: #555;
    }
    &:after {
      background-color: #555;
    }
    &:hover {
      background-color: #159;
      transition: 0.3s ease-out;
      &:before {
        background-color: #159;
        transition: 0.3s ease-out;
      }
      &:after {
        background-color: #159;
        transition: 0.3s ease-out;
      }
    }
  }
}
.tabs:last-child{
    -webkit-transform: skewX(0deg);
    transform: skewX(0deg);
  }
span {
  display: inline-block;
  width: 150px;
  text-align: center;
  height: 50px;
  line-height: 50px;
  z-index: 3;
}

#page {
  background-color: white;
  height: calc(100vh - 120px);
  width: calc(100vw - 61px);
  position: relative;
  top: 10px;
  left: 1px;
  padding: 30px;
}

SassMeister-output.css

body {
  background-color: #000;
  margin: 0;
  padding: 0;
  font-family: sans-serif;
  font-size: 16px;
}

.tab {
  height: 50px;
  width: 150px;
  background-color: #FFF;
  position: relative;
  top: 10px;
  left: 30px;
  display: inline-block;
  z-index: 2;
}
.tab.active:before {
  background-color: white;
}
.tab.active:after {
  background-color: white;
}
.tab:before {
  height: 50px;
  width: 30px;
  content: "";
  position: absolute;
  left: -15px;
  top: 0px;
  -webkit-transform: skewX(-30deg);
  transform: skewX(-30deg);
  z-index: -1;
}
.tab:after {
  height: 50px;
  width: 30px;
  content: "";
  position: absolute;
  left: 135px;
  top: 0px;
  -webkit-transform: skewX(-30deg);
  transform: skewX(-30deg);
  z-index: -1;
}
.tab:nth-of-type(2) {
  background-color: #555;
  top: 10px;
  left: 56px;
  z-index: 1;
  color: #EEE;
}
.tab:nth-of-type(2):before {
  background-color: #555;
}
.tab:nth-of-type(2):after {
  background-color: #555;
}
.tab:nth-of-type(2):hover {
  background-color: #159;
  transition: 0.3s ease-out;
}
.tab:nth-of-type(2):hover:before {
  background-color: #159;
  transition: 0.3s ease-out;
}
.tab:nth-of-type(2):hover:after {
  background-color: #159;
  transition: 0.3s ease-out;
}

.tabs:last-child {
  -webkit-transform: skewX(0deg);
  transform: skewX(0deg);
}

span {
  display: inline-block;
  width: 150px;
  text-align: center;
  height: 50px;
  line-height: 50px;
  z-index: 3;
}

#page {
  background-color: white;
  height: calc(100vh - 120px);
  width: calc(100vw - 61px);
  position: relative;
  top: 10px;
  left: 1px;
  padding: 30px;
}

SassMeister-rendered.html

<nav id="tabs">
  <div class="tab active">
    <span>Tab 1</span>
  </div>
  <div class="tab">
    <span>Tab 2</span>
  </div>
</nav>
<div id="page">
  Lorem Ipsum dolor sit amet ...
</div>