Draw Curved Line and Filter Drop Shadow

Demo: https://codepen.io/th-i-duy-khang/pen/ExmEoRQ

HTML

<div class="box"></div>

CSS

.box{
  width:1000px; height:100px;  
  border:solid 5px #000;
  border-color:#ff6565 transparent transparent transparent;
  border-radius: 50%/100px 100px 0 0;
  filter:drop-shadow(3px 3px 10px #ff6565);
}