* {
    box-sizing: border-box;
    user-select: none;
    margin: 0;
    padding: 0;
}

html,
body {
    display: grid;
    height: 100%;
    place-items: center;
}

body {
    background: url('images/gradient.jpg') center center;
    background-size: cover;
}

.container {
    position: relative;
    width: 500px;
    height: 300px;
    overflow: hidden;
    border-radius: 7px;
    cursor: ew-resize;
}

.container img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    display: block;
}

.mask {
    position: absolute;
    top: 0;
    left: 0;
    height: 100%;
    width: 50%;
    backdrop-filter: blur(5px);
    -webkit-backdrop-filter: blur(5px);
    border-right: 2px solid rgba(255, 255, 255, 0.6);
    z-index: 2;
}

.mask:after {
    content: '< >';
    position: absolute;
    top: 50%;
    right: 0;
    transform: translate(50%, -50%);
    background: rgba(0, 0, 0, 0.5);
    color: #fff;
    padding: 10px;
    border-radius: 50%;
    font-size: 14px;
    font-weight: bold;
    pointer-events: none;
}