Internet Explorer ignores background-color with flex property

I have an HTML document with a form. In the body I have a div to container mode where I enclose the form (to limit the width of it).

To make it responsive I use flex, my problem arises with Internet Explorer. The color of the body is # F2F2F2, while the background-color of the container is white (#FFF).

Google Chrome and Firefox correctly interpret the container's background color and display it, but Internet Explorer ignores it. It is solved when I remove the flex property.

body{
    background: #F2F2F2;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

.contenedor{
    margin: auto;
    width: 90%;
    max-width: 1200px;
    background-color: #FFF !important;
    -webkit-flex: 1;
    -ms-flex: 1;
    flex: 1;
}