I want the menu in Mobirise's project could appear from the left side but I can't find any option like that.

I tried the code below but it didn't work.

.sidenav {
  height: 100%; 
  width: 0; 
  position: fixed; 
  z-index: 1; 
  top: 0; 
  left: 0;
  background-color: #111; 
  overflow-x: hidden; 
  padding-top: 60px; 
  transition: 0.5s;
}

.sidenav a {
  padding: 8px 8px 8px 32px;
  text-decoration: none;
  font-size: 25px;
  color: #818181;
  display: block;
  transition: 0.3s;
}

.sidenav a:hover {
  color: #f1f1f1;
}

.sidenav .closebtn {
  position: absolute;
  top: 0;
  right: 25px;
  font-size: 36px;
  margin-left: 50px;
}

I've seen this question before and it appears as it stands this system does not do that. On top of that it appears Mobirise's own forum and support is failing the users. The more I read about Mobirise the less impressed I am. Maybe it's time to try another system that does what you want?