Add and Colour an SVG background
#swipebox-next { background-color: #000; mask: url('../images/Arrow.svg') no-repeat 50% 50%; -webkit-mask: url('../images/Arrow.svg') no-repeat 50% 50%; }
Add SVG background with the default color and set the width and height
#swipebox-close { background-image: url('../images/Close_Black.svg'); background-position: center; background-size: cover; right: 30px; top: 15px; width: 30px; height: 30px; }