.dino {
    position: absolute;
    background-image: url(mouse.png);
    background-repeat: no-repeat;
    background-size : 100% 100%;
    width: 60px;
    height: 60px;
    bottom: 0px;
}

.obstacle {
    position: absolute;
    background-image: url(trap.png);
    background-repeat: no-repeat;
    background-size : 100% 100%;
    width: 60px;
    height: 60px;
    bottom: 0px;
}

#bg {
    position: fixed; 
    top: -50%; 
    left: -50%; 
    width: 200%; 
    height: 200%;
    z-index:-1;
}

#bg img {
    position: absolute; 
    top: 0; 
    left: 0; 
    right: 0; 
    bottom: 0; 
    margin: auto; 
    min-width: 50%;
    min-height: 50%;
}

h1#alert {
    text-align: center;
    margin-top: 300px;
    font-family: 'Courier New', Courier, monospace;
    animation-name: flash;
    animation-duration: 0.2s;
    animation-timing-function: linear;
    animation-iteration-count: infinite;
    animation-direction: alternate;
    animation-play-state: running;
}

@keyframes flash {
    from {color: red;}
    to {color: black;}
}