<div class="slick-slide"><div class="container-content">слайд 1</div></div>
<div class="slick-slide slick-current"><div class="container-content">слайд 2</div></div>
<div class="slick-slide"><div class="container-content">слайд 3</div></div>
.slick-current > .container-content {
transform: scale(2);
}