Viết game bắn chim bằng CSS Animation không cần JS

Mình tham khảo được cách viết game bằng css animation mà không cần sử dụng JS trên mạng nên giới thiệu cho những ai chưa biết ạ. (bow)

• Đầu tiên các bạn add html như bên dưới:

<div class="wrapper">
  <div class="timer">
       <span></span>    
  </div>
  <div class="gameover">GAME OVER</div>
  <h1>KILL THE BIRDS <span>(shoot the birds)</span></h1>
  <h2>CSS GAME - NO JS!</h2>
  <input class="input-circle input-circle1" type="radio" id="circle1" >
 <input class="input-circle input-circle2" type="radio" id="circle2" >
 <input class="input-circle input-circle3" type="radio" id="circle3" >
 <input class="input-circle input-circle4" type="radio" id="circle4" >
 <input class="input-circle input-circle5" type="radio" id="circle5" >
 <input class="input-circle input-circle6" type="radio" id="circle6" >
  
  <label for="circle1" class="pajaro pajaro1"><span></span></label>
  <label for="circle2" class="pajaro pajaro2"><span></span></label>
  <label for="circle3" class="pajaro pajaro3"><span></span></label>
  <label for="circle4" class="pajaro pajaro4"><span></span></label>
  <label for="circle5" class="pajaro pajaro5"><span></span></label>
  <label for="circle6" class="pajaro pajaro6"><span></span></label>
  <div class="sum">SCORE:</div>
</div>

• Sau đó các bạn add css như sau:

body{
  counter-reset:birds;
  -webkit-touch-callout: none;
-webkit-user-select: none;
-khtml-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
user-select: none;
  overflow:hidden;
}
/*hide checkbox*/
input{position:fixed; left:-10px; top:-10px;}

h1{margin:0; text-align:center;}
h2{position:fixed; right:20px; bottom:0; font-size:18px; color:red;}

/*play area*/
.wrapper{  
  height:500px;
  background: -webkit-linear-gradient(top, hsla(210,70%,80%,1) 0%,hsla(210,50%,100%,1) 100%);
  position:relative;
  cursor:crosshair;
}
/*count dead birds*/
.input-circle:checked{
  counter-increment:birds;
}

.sum{position:fixed; left:45%; top:60px; font-size:24px; fonot-weight:bold;}

/*print to screen dead birds*/
.sum:after{
  content: counter(birds);
}

.input-circle ~ .pajaro{
  opacity:0;
  transition:0.3s  cubic-bezier(0,.43,1,0);
  animation: move 8s infinite alternate;
}
.input-circle1:not(:checked) ~ .pajaro1,
.input-circle2:not(:checked) ~ .pajaro2,
.input-circle3:not(:checked) ~ .pajaro3,
.input-circle4:not(:checked) ~ .pajaro4,
.input-circle5:not(:checked) ~ .pajaro5,
.input-circle6:not(:checked) ~ .pajaro6
{
  opacity:1; 
}


.input-circle1:checked ~ .pajaro1 span,
.input-circle2:checked ~ .pajaro2 span,
.input-circle3:checked ~ .pajaro3 span,
.input-circle4:checked ~ .pajaro4 span,
.input-circle5:checked ~ .pajaro5 span,
.input-circle6:checked ~ .pajaro6 span
{
  display:block;
  
}

.pajaro{   
  position:absolute;
  left:0;  
  cursor:crosshair;
}
.pajaro>span{
  display:none;position:absolute; z-index:2; left:-250%;bottom:-50%;  
  background-color:white; border:solid 2px #000; awidth:80px; height:30px; padding:10px; border-radius:50%;
}
.pajaro>span:before{
  content:"I'm Dead!"; color:red; font-weight:bold;
}

.pajaro1{top:50px;
  animation-delay: -2s!important;
  transform:scale(0.9);
}
.pajaro2{
  top:100px;
  animation-delay: -4s!important;
  transform:scale(0.5); 
}
.pajaro3{
  top:200px;
  animation-delay: -3s!important;
  transform:scale(1.4); 
}

.pajaro4{top:50px;
  animation-delay: -12s!important;
  transform:scale(0.9);
}
.pajaro5{
  top:100px;
  animation-delay: -16s!important;
  transform:scale(0.5); 
}
.pajaro6{
  top:200px;
  animation-delay: -20s!important;
  transform:scale(1.4); 
}

@keyframes move{
0%{left:0%;}
20%{left:20%;top:50%; }
40%{top:30%; left:60%;}
60%{top:80%;left:80%;}
80%{top:10%; left:20%:}
100%{top:30%; left:20%; }
}


.timer{
  background-color:#333; awidth:300px;height:50px;
  position:fixed;
}


.timer span{
  display:block;
  background:repeating-linear-gradient(-45deg, #000, rgba(0, 0, 0, 0) 25px, #FFF 25px, #FFF 50px);
  awidth:300px; height:50px;
  animation:timer 20s linear;
}

.timer span:before{  
  content:"TIME LEFT";
  display:block;
  position:absolute; z-index:3;
  left:0; 
  right:0;
  top:0;
  bottom:0;
  text-align:center;
  line-height:50px;
  font-size:25px;
  color:red;
}
@keyframes timer{
0%{awidth:10px;}
100%{awidth:300px; display:block;}
}


.gameover{
  position:fixed; z-index:100000; left:0; top:0; bottom:0; right:0; background-color:rgba(0,0,0,0.8);
  animation:gameover 20s linear forwards;
  font-size:80px; color:white; font-weight:bold; text-align:center; 
  text-indent:0;  
  line-height:500px;
}

@keyframes gameover{
0%{left:-5000px;bottom:100%;}
97%{left:-5000px;bottom:100%;}
100%{ left:0px;}
}

/*------------------------------------------------------ body of the bird
*/

.pajaro{
  background:black;
  border-radius: 50% 50% 20% 20%;
  color:white;
  line-height:20px;
  letter-spacing: 2px;
  font-size:0.8em;
  text-align:center;
  position:absolute;
 
  margin-top:-20px; margin-left:-10px;
  awidth:15px; height:15px;
  animation:planeo 0.8s linear infinite;
  z-index:999;
}

.pajaro:after,
.pajaro:before{
  content:"";
  position:absolute;
  top:50%; left:50%;
}

/*------------------------------------------------------ bird wings
*/

.pajaro:after{
  border-radius: 100% 100% 0 0;
  box-shadow: inset 0px 5px 0 black;
  awidth:100px; height:100px;
  margin-top:-7px; margin-left:-50px;
  transform-origin: 100% 0%;
  animation:alas 3s linear infinite;
}

/*------------------------------------------------------ bird beak
*/

.pajaro:before{
  background:#FFC37F;
  border-radius: 100% 0% 20% 0%;
  margin-top:3px; margin-left:-4px;
  awidth:6px; height:6px;
  transform:rotateZ(45deg);
}

/*------------------------------------------------------ wings animation
*/

@keyframes alas {
  50%{
    transform:rotateX(-1440deg);
  }
}

/*------------------------------------------------------ bird animation
*/

@keyframes planeo {
  40%{
    transform:rotateZ(2deg) translateX(2px) translateY(10px) translateZ(0);
    line-height:16px;
    font-size:0.6em;
  }
  80%{
    transform:rotateZ(-2deg) translateX(5px) translateY(8px) translateZ(0);
  }
}