style.css

body {
    /* width:96%; */
}

.field {
  width: 30px;
  height: 30px;
  background-color: red;
  margin: 2px;
  position: relative;
}

.hide {
  cursor: pointer;
  position:absolute;
  left: 0;
  top: 0;
  z-index: 1;
  width: 30px;
  height: 30px;
  background-color: blue;
  margin: 0;
}

.hide:hover {
  background-color: #3399ff;
}

.elem {
  cursor: default;
  padding-top: 5px;
  color: white;
}

#game {
  width: 306px;
  margin-left: auto;
  margin-right: auto;
  margin-top: 30px;
}

.start {
  cursor: pointer;
  background-color: red;
  color: white;
  width: 302px;
  height: 50px;
  margin-left: auto;
  margin-right: auto;
  margin-top: 30px;
}

.start:hover {
  background-color: #ff3939;
}

.start p {
  padding-top: 15px;
  padding-left: 80px;
}

.startwindow {
  width: 302px;
  height: 302px;
  margin: 2px;
  background-color: red;
}

.startwindow img {
  width: 140px;
  margin-left: 80px;
}

h1 {
  color: white;
  padding-top: 40px;
  padding-bottom: 10px;
  margin-left: 100px;
}