style.css

@import url('https://fonts.googleapis.com/css2?family=Muli&display=swap');

* {
    box-sizing: border-box;
}

:root{
    --line-border-fill: #3498db;
    --line-border-empty:#e0e0e0;
}
body{
    background-color: #f6f7fb;
    font-family: 'Muli', sans-serif;
    display: flex; 
    flex-direction: column;
    align-items: center;
    justify-content: center;
    height: 100vh; 
    overflow: hidden;
    margin: 0;
}

.container{
    text-align: center;
}

.progress-container{
    display: flex;
    justify-content: space-between; /* to take up the whole width with space in between */
    position: relative;
    margin-bottom: 30px;
    max-width: 100%;
    width:350px;
}

/* Default Line */
.progress-container::before {
    content:'';
    background-color: var(--line-border-empty); 
    position:absolute;
    top:50%;
    left: 0;
    transform: translateY(-50%); /* have the line cross the middle */
    height: 4px;
    width:100%;
    z-index: -1; /* have the line behind the circles */
    transition: 0.4s ease;
}

/* Line */
.progress {
    background-color: var(--line-border-fill); 
    position:absolute;
    top:50%;
    left: 0;
    transform: translateY(-50%); /* have the line cross the middle */
    height: 4px;
    width:0%;
    z-index: -1; /* have the line behind the circles */
    transition: 0.4s ease;
}

.circle{
    background-color: #fff;
    color:#999;
    border:3px solid  var(--line-border-empty);
    border-radius: 50%;
    width:30px;
    height:30px;
    display:flex;
    align-items: center; /* vertical center */
    justify-content: center; /* horizontal center */
    transition: 0.4s ease;
}

.circle.active{
    background-color: #3498db;
    color:#fff;
    border-color: var(--line-border-fill);
}

.btn{
    background-color: var(--line-border-fill);
    border-radius: 5px;
    color:#fff;
    cursor: pointer;
    border: 0;
    font-family:inherit;
    padding: 8px 30px;
    margin:5px;
    font-size:14px;
}
.btn:active{
    transform:scale(0.98)
}

.btn:focus{
    outline:0;
}
.btn:disabled{
    background-color: var(--line-border-empty);
    cursor:not-allowed;
}