Mweb 635

@RafLeszczynski @nandy-andy @rogatty This makes us get rid of the hardcoded filterbox width with animation still being smooth :)
The width is imposed by the parent anyway (245px for desktop, 100% for mobile). It is set for this element for desktop at 225 px (-2x10px of padding) and at 100% for mobile to let the browser calculate the animation smoothly.