html, body {
    margin: 0;
    padding: 0;
}

:root {
    --progressbar-bg: lightgrey;
    --start: red;
    --middle: blue;
    --finish: green;
} 

.container { 
    position: relative;
    height: 100vh; 
    width: 100vw;
    display: flex;
    justify-content: center;
    align-items: center;
    background: #CAF4F4;
}

/* outer progress bar */
.progress-bar {
    position: relative;
    width: 400px;
    height: 40px;
    background: var(--progressbar-bg);
    border-radius: 30px;
    box-shadow: rgba(100, 60, 0, 0.55) 0px 4px 4px;
    overflow: hidden;
    z-index: 1;
}

/* inner progress bar */
.progress-status {
    position: absolute;
    width: 100%; /* set to 100% to fill the outer progress bar */
    height: 100%;
    border-radius: 30px;
    z-index: 2;
    /* background: linear-gradient(to left, var(--start), var(--middle), var(--finish)); */
    /* animation: name duration timing-function delay iteration-count direction fill-mode play-state;
 */
    /* animation: barAnimation 5s linear 3s infinite; --> delay works only at the start 1x ands stops delaying because it's infinite */
    animation: barAnimation 5s linear infinite; 
    background: linear-gradient(to left, var(--start), var(--middle), var(--finish));
    /* background-size: 300% 100%;  */
}


@keyframes barAnimation {
    0% {
        width: 0%;
        background: var(--start);
    }
    25% {
        width: 25%;
        background: var(--start);
    }
     45% {
        width: 45%;
        background: var(--middle);
    }
    65% {
        width: 65%;
        background: var(--middle);
    }
    85% {
        width: 100%;
        background: var(--finish);
        /* transition, creates pause effect */
    }
    100% {
        width: 100%;
        background: var(--finish);
    }
}