Change backround on h5p-content

Hi!!! im trying to change the color of the backround  from white to black, i tried using the style sheet of wordpress and changing the code of the pluging in styles>h5p.css It worked in pc but doesn't on mobile. Please help!!!

.h5p-content {

  position: relative;

  background: #000000;

  border: 1px solid #EEE;

  border-bottom: none;

  box-sizing: border-box;

  -moz-box-sizing: border-box;