style.css

* {
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}

:root {
    --background-color: #F6F7FB;
    --primary-color: #4C426D;
}

body {
    overflow: hidden;
    background-color: white;
    font-family: Verdana, Arial, sans-serif;
    font-size: 13px;
}

.chat-item {
    padding: 15px 10px;
    border-bottom: 1px solid var(--background-color);
}

.info-avatar,
.avatar {
    width: 30px;
    height: 30px;
    border-radius: 9999px;
    background-color: darkgrey;
    float: left;
    margin-right: 15px;
}


.info-avatar {
    width: 100px;
    height: 100px;
    text-align: center;
    float: none;
    margin: 50px auto 0;
}

.info-name {
    text-align: center;
    font-size: 22px;
    font-weight: bold;
    margin-top: 15px;
}

.info-description {
    margin: 20px 0;
    text-align: center;
}

.chat-message {
    border: 1px solid var(--background-color);
    border-radius: 20px 0 20px 20px;
    margin-bottom: 15px;
    padding: 20px;
    width: calc(100% - 40px);
    background-color: var(--background-color);
}

.chat-message:nth-child(2n) {
    margin-left: 40px;
    border-top-left-radius: 0;
    border-top-right-radius: 20px;
    background-color: var(--primary-color);
    color: white;
}


.left, .middle, .right {
    background-color: white;
    position: absolute;
    top: 0;
    bottom: 0;
    width: 100%;
    overflow-y: scroll;
    padding: 15px;
    border-radius: 20px;
}

.left {
    cursor: pointer;
}

.middle, .right {
    transition: transform .2s;
    transform: translateX(100%);
}

.middle {
    padding-top: 40px;
}

.right.show,
.middle.show {
    transform: translateX(0);
}


.button-wrapper {
    position: absolute;
    width: 100%;
    display: flex;
    justify-content: space-between;
    left: 0;
    top: 15px;
    padding: 0 15px;
}


@media screen and (min-width: 768px) {
    #back-button {
        display: none;
    }

    .left {
        width: 300px;
    }

    .middle {
        transform: translateX(0);
    }

    .middle, .right {
        width: calc(100% - 300px);
        left: 300px;
    }
}

@media screen and (min-width: 1024px) {
    .left {
        width: 400px;
    }

    .middle {
        width: calc(100% - 800px);
        left: 400px;
    }

    .right {
        transform: translateX(0);
        width: 400px;
        left: unset;
        right: 0;
    }

    #info-button,
    #close-button {
        display: none;
    }
}