JSFiddle - React, Tailwind, and code Playground

HTML

<div id="tab12" class="tab-12" onclick="init() " >
   12
   <div class="done-course">
       done course
   </div>
</div>
 <div id="tab3" class="tab-3">
    3
    <div class="unfinished-course">
unfinished course
    </div>
                                                                </div>

CSS

.tab-12 {
    border-top: 1px solid rgb(222, 225, 226);
    font-size: 34px;
    font-family: "ProximaNova";
    color: rgb(230, 115, 51);
    font-weight: bold;
    text-transform: uppercase;
    text-align: center;
    width: 100%;
    height: 80px;
}

.done-course {
    font-size: 12px;
    font-family: "ProximaNova";
    color: rgb(230, 115, 51);
    text-transform: uppercase;
    line-height: 1.5;
    text-align: center;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.tab-3 {
    width: 100%;
    height: 80px;
    font-size: 34px;
    font-family: "ProximaNova";
    color: rgb(149, 165, 166);
    font-weight: bold;
    text-transform: uppercase;
    text-align: center;
    background-color: #ecf0f1;
    border-top: 1px solid #ecf0f1;
    border-right: 1px solid #ecf0f1;
    border-bottom: 1px solid #e5e5e5;
    border-left: 1px solid #e5e5e5;
}

.unfinished-course {
    font-size: 12px;
    font-family: "ProximaNova";
    color: rgb(149, 165, 166);
    text-transform: uppercase;
    line-height: 1.5;
    text-align: center;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

JavaScript

function init() {
    var tab12 = document.getElementById("tab12");
    var tab3 = document.getElementById("tab3");
    tab3.addEventListener("click", function(){
  this.style.color = 'rgb(230, 115, 51)';
  this.style.backgroundColor = 'rgb(255,255,255)';
  tab12.style.color = 'rgb(149, 165, 166)';
  tab12.style.backgroundColor = '#ecf0f1';
})
tab12.addEventListener("click", function(){
  this.style.color = 'rgb(230, 115, 51)';
  this.style.backgroundColor = 'rgb(255,255,255)';
  tab3.style.color = 'rgb(149, 165, 166)';
  tab3.style.backgroundColor = '#ecf0f1';
})
  }