<div class="container">
    <div class="title plain">Plain</div>
    <div class="bar">
        <span class="bar-unfill">
            <span class="bar-fill"></span>
        </span>
     </div>
</div>
body {
  margin: 5%;
}
.container {
    width:30%;
    margin:0 auto
}

.title {
    background:#545965;
    color:#fff;
    padding:15px;
    float:left;
    position:relative;
    -webkit-border-top-left-radius:5px;
    -webkit-border-bottom-left-radius:5px;
    -moz-border-radius-topleft:5px;
    -moz-border-radius-bottomleft:5px;
    border-top-left-radius:5px;
    border-bottom-left-radius:5px
}
.bar-unfill {
    height:15px;
    display:block;
    background:#fff;
    width:100%;
    border-radius:8px
}
.bar-fill {
    height:15px;
    display:block;
    background:#45c9a5;
    width:0;
    border-radius:8px;
    -webkit-transition:width .8s ease;
    -moz-transition:width .8s ease;
    transition:width .8s ease;
    -webkit-animation:progressbar 7s infinite;
    animation:progressbar 7s infinite
}
/* Chrome, Safari, Opera */
@-webkit-keyframes progressbar { 
    from {
        width:0
    }
    to {
        width:100%
    }
}
/* Standard syntax */
@keyframes progressbar {
    from {
        width:0
    }
    to {
        width:100%
    }
}

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.