<div class="eq-c">
  <var>S</var> =
  <span class="intsuma">
    <span class="lim">5</span>
    <span class="sum-frac">&sum;</span>
    <span class="lim"><var>n</var>=0</span>
  </span>
  <div class="fraction">
     <span class="fup">(<var>x</var> + 1)
       <sup><var>n</var></sup>
     </span>
    <span class="bar">/</span>
    <span class="fdn"><var>n</var></span>
  </div>
</div>

// Body
body{
  position: absolute;
  top: 50%; left: 50%;
  transform: translate(-50%, -50%);
  font-size: 2rem;
  text-align: center;
}

// Sum
.intsuma {
  position: relative;
  display: inline-block;
  vertical-align: middle;
  text-align: center;
}
.intsuma > span {
  display: block;
  font-size: 70%;
}
.intsuma .lim-up {
  margin-bottom: -1.0ex;
}
.intsuma .lim {
  margin-top: -0.5ex;
}
.intsuma .sum {
  font-size: 1.5em;
  font-weight: lighter;
}
.intsuma .sum-frac {
  font-size: 1.5em;
  font-weight: 100;
}

.fraction {
    display: inline-block;
    vertical-align: middle; 
    margin: 0 0.2em 0.4ex;
    text-align: center;
  & > span {
    display: block;
    padding-top: 0.15em;
  }
  & span{
    &.fdn {
      border-top: thin solid black;
    }
    &.bar {
      display: none;
    }
  }
}