CSS

make a half ciricle with div

div {
  width: 300px;
  height: 300px;
  position: relative;
  overflow: hidden;
}

div::before {
  content: '';
  position: absolute;
  bottom: 50%;
  width: 100%;
  height: 100%;
  border-radius: 100%;
  box-shadow: 0px 300px 0px 300px #448CCB;
}