body {
  margin: 0;
} .mainImg {
  background-color: rgb(125, 125, 125);
  position: fixed; 
  top: -50%; 
  left: -50%; 
  width: 200%; 
  height: 200%;
} .mainImg svg {
  position: absolute; 
  top: 0; 
  left: 0; 
  right: 0; 
  bottom: 0; 
  margin: auto; 
  min-width: 50%;
  min-height: 50%;
}

#c_sech, #c_minh, #c_hrh, #secondhand, #minutehand, #hourhand, #c_sech_shadow, #secondhand_shadow, #minutehand_shadow, #hourhand_shadow{
  transform-box: fill-box;
  transform-origin: center;
}

@media (max-width: 768px) {
  .mainImg svg{
    height: 220%;
    width: 220%;
    transform: translateX(-26%);
  }
}