responsive issue

Hi,
I have some issue with responsive aspect of the plugin (basic slideshow gallery) since last update.
I set the dimensions for the gallery 1200px x 480px.
With a desktop computer, no problem : images are correctly resized, proportions are respected.
With smaller screens, images are correctly resized with correct proportions but the div. #ngg-image… has WRONG PROPORTIONS : 940×480 px (instead of 940×376), 748×480 px (instead of 748×300) and finally 300×400 px (instead of 300×120).
Therefore, there is an empty white space above the images of the slideshow, with only the arrows.
Before the update, i used a custom css to solve it, but it does not work any more.
Any idea to solve it now ?

@media only screen and ( max-width: 1200px ){
.ngg-slideshow {
width: 940px;
height: 376px;
}
.image-placeholder {
width: 940px;
height: 376px;
}
}
@media only screen and ( max-width: 960px ){
.ngg-slideshow {
width: 940px;
height: 376px;
}
.image-placeholder {
width: 748px;
height: 300px;
}

}
@media only screen and ( max-width: 767px ){
.ngg-slideshow {
width: 940px;
height: 376px;
}
.image-placeholder {
width: 300px;
height: 120px;
}
}

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