JSFiddle - React, Tailwind, and code Playground

HTML

<div class='outer'>
    <div class='inner' id="inner1"></div>
</div>

<div class='outer'>
    <div class='inner' id="inner2"></div>
</div>

<div class='outer'>
    <div class='inner' id="inner3"></div>
</div>

<div class='outer'>
    <div class='inner' id="inner4"></div>
</div>

CSS

.outer {
    border: 1px solid black; 
    width: 450px;
    height: 30px;
    -moz-border-radius: 25px;
    margin-bottom: 20px;
}

.inner {
    background: red;
    height: 100%;
    -moz-border-radius: 25px;
}

#inner1 {
    width: 30%;
}

#inner2 {
    width: 99%;
}

#inner3 {
    width: 30%;
    -moz-border-radius: 25px 0px 0px 25px;
}

#inner4 {
    width: 100%;
    -moz-border-radius: 25px 25px 25px 25px;
}

JavaScript

$('#inner4')
    .css('width',25)
    .css('-moz-border-radius-topright','0')
    .css('-moz-border-radius-bottomright','0')
    .animate(
      {
        width:425
      }, 
      3000, 'linear',
      function() {
          $('#inner4').animate({
            width:450,
            '-moz-border-radius-bottomright':'+=25',
            '-moz-border-radius-topright':'+=25'
          },
          200,'linear',
          function() {}
        );//end inner animate
      }
    );//end animate