* {
            box-sizing: border-box;
        }

        body {
            font-family: "Trebuchet MS", "Lucida Sans Unicode", sans-serif;
            margin: 0;
        }

        section {
            min-height: 100vh;
            display: flex;
            justify-content: center;
            align-items: center;
        }

        section:first-child {
            background-color: #aaa;
        }

        section:nth-child(2) {
            background-color: #bbb;
        }

        section:nth-child(3) {
            background-color: #ccc;
        }

        section:last-of-type {
            background-color: #eee;
        }

        .progress {
            position: relative;
            width: 500px;
            height: 30px;
            background-color: white;
            margin: 10px;
        }

        .progress span {
            position: absolute;
            left: 0;
            top: 0;
            height: 100%;
            background-color: indianred;
            transition: width 0.3s linear;
        }