Game made with only HTML and CSS - https://news.ycombinator.com/item?id=10903691

game.css

html, body {
  margin: 0;
  padding: 0;
  height: 100%;
  width: 100%;
  overflow: hidden;
  text-align: center;
  font-family: sans-serif;
  background: #333;
  color: #fff;
  text-transform: uppercase;
}

a {
  color: tomato;
}

svg {
  position: absolute;
}


#game {
  position: relative;
  width: 800px;
  height: 600px;
  margin: 20px auto 40px;
  box-shadow: 0 1px 15px #222;
  overflow: hidden;
  -webkit-transform: perspective(200px) rotateX(15deg) translateY(-90px);
          transform: perspective(200px) rotateX(15deg) translateY(-90px);
  cursor: url('http://victordarras.fr/cssgame/vessel.png'), auto;
}


#gameover,
#win {
  position: absolute;
  top: 0;
  left: 0;
  height: 100%;
  width: 100%;
}

#gameover {
  display: none;
  background: tomato;
}
#win {
  opacity: 0;
  pointer-events: none;
}

#start-spot {
  position: absolute;
  bottom: 10px;
  left: 50%;
  width: 20px;
  height: 20px;
  -webkit-transform: translateX(-50%);
          transform: translateX(-50%);
  background: #fff;
}

.wall-left,
.wall-right {
  position: absolute;
  bottom: 0;
  width: 100%;
  height: 400%;
  background: linear-gradient(#fff,#777);
  transform: translateZ(1px);
}
.wall-left {
  left: 0;
  /*-webkit-clip-path: polygon(0 0, 40% 0, 35% 15%, 55% 35%, 45% 45%, 60% 60%, 30% 80%, 40% 100%, 0 100%);*/
  -webkit-clip-path: url('#left');
  clip-path: url('wall.svg#left');
}
.wall-right {
  right: 0;
  /*-webkit-clip-path: polygon(60% 0, 100% 0, 100% 100%, 60% 100%, 44% 81%, 70% 60%,57% 44%, 65% 35%,  46% 15%);*/
  -webkit-clip-path: url('#right');
  clip-path: url('wall.svg#right');
}

#game:hover .wall-left,
#game:hover .wall-right {
  -webkit-animation: wallScroll 10s ease-in forwards;
          animation: wallScroll 10s ease-in forwards;
}
#game:hover #win {
  -webkit-animation: win 10s linear forwards;
          animation: win 10s linear forwards;
}

#game:hover #start-spot {
  display: none;
}

.wall-left:hover ~ #gameover,
.wall-right:hover ~ #gameover,
#gameover:hover {
  display: block;
  z-index: 1;
}


/* Quelques styles pour la forme */
#gameover h1,
#win h1 {
  position: absolute;
  top: 50%;
  left: 50%;
  -webkit-transform: translate3d(-50%, -50%, 0);
          transform: translate3d(-50%, -50%, 0);
}
.instructions {
  font-weight: lighter;
}

/* Les keyframes en bas de document, par convention */


@keyframes wallScroll {
  0% {
    transform: none;
  }
  100% {
    transform: translateY(100%);
  }
}


@keyframes win {
  0% {
    opacity: 0;
  }
  99% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}

game.html

<svg>
    <defs>
        <clipPath id="left">
        <path d="M208.051459,2400 C263.281717,2400 309.415831,2355.25297 311.095095,2300.04788 L312.664062,2248.46875 L237.390625,2194.82812 L137.777344,2030.35938 L237.390625,1931.83594 L201.117188,1718.30469 L512.40625,1671.47266 L625.328125,1623.67187 L554.5,1528.82813 L554.671875,1367.17188 L505.5,1496.0625 L389.328125,1318.78125 L308.054687,1456.08984 L292.945312,1260.08984 L139.835938,1239.41797 L193.140625,968.167969 L594.265625,834.582031 L589.878906,810.363281 L294.828125,639.890625 L466.5625,514 L286.109375,421.609375 L403.671875,259.953125 L307.732398,87.3968996 C280.895903,39.1289248 214.371469,-1.77635684e-15 159.13546,-1.77635684e-15 L0,-1.77635684e-15 L0,2400 L208.051459,2400 Z" id="path-1" sketch:type="MSShapeGroup"></path>
        </clipPath>
        <clipPath id="right">
        <path d="M607.571488,2400 C552.344521,2400 500.243973,2355.8417 491.198356,2301.34979 L477.292969,2217.58203 L322.253906,2136.07031 L277.097656,2050.32031 L335.421875,1981.23438 L322.253906,1799.02734 L555.867188,1774.47266 L740.628906,1650.70703 L634.464844,1501 L606.171875,1092.44531 L489.804688,1280.52734 L455.144531,1174.73438 L363.847656,1236.04297 L393.441406,1148.53906 L268.179688,1157.70312 L292.765625,1043.58203 L708.695312,919.421875 L669.171875,751.890625 L442.472656,634.820312 L614.207031,508.929688 L400,400.347656 L477.292969,265.375 L508.251674,98.3209413 C518.314845,44.0197848 571.238285,-1.77635684e-15 626.48025,-1.77635684e-15 L800,-1.77635684e-15 L800,2400 L607.571488,2400 Z" id="path-2" sketch:type="MSShapeGroup"></path>
        </clipPath>
    </defs>
</svg>

  <div id="game">
    <div id="start-spot"></div>
    <div class="wall-left"></div>
    <div class="wall-right"></div>

    <div id="gameover"><h1>You lose</h1></div>
    <div id="win"><h1>Congratulations !<br/>You win</h1></div>
  </div>

  <p class="instructions">
    Place your cursor on the white dot to start.<br/>
    Avoid the walls and escape !<br/>
    <em>(Chrome/Chromium only)</em>
  </p>

  <p>
    <a href="https://twitter.com/share" class="twitter-share-button"{count} data-text="An awesome HTML & CSS game !" data-via="victordarras" data-hashtags="css">Tweet</a>
    <script>!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https';if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src=p+'://platform.twitter.com/widgets.js';fjs.parentNode.insertBefore(js,fjs);}}(document, 'script', 'twitter-wjs');</script>
  </p>

  <p class="instructions"><small>
    Game created by <a href="/">Victor Darras</a> only with <b>CSS & HTML</b> !<br/>
    <a href="http://www.synbioz.com/blog/css_shape_et_mini_jeu" >HOW ? (in french)</a>
  </small></p>