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CSS

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HTML 

              
                <section class="stage">

    <svg height="390" width="550" id="mountains">
        <polygon points="300,390 190,90 320,130 400,340" fill="#5d2042" />
        <polygon points="0,340 108,190 194,100 201,120 301,390" fill="#320e40" />
        <polygon points="14,348 117,174 194,102 172,377" fill="#3b1642" fill-opacity="0.8" />
        <polygon points="120,174 194,102 233,206 144,275" fill="#3d1744" fill-opacity="0.9" />

        <polygon points="233,206 288,177 324,214" fill="#421943" />
        <polygon points="233,206 324,214 247,245" fill="#3e1743" />
        <polygon points="247,245 324,214 360,360" fill="#411842" />
        <polygon points="324,214 288,177 350,210" fill="#632242" />
        <polygon points="324,214 350,210 360,360" fill="#652343" />

        <g id="apex">
            <polygon points="108,190 170,40 194,100" fill="#aeacb9" />
            <polygon points="170,40 234,6 260,70 288,178 194,102" fill="#ceced8" />
            <polygon points="234,6 290,80 320,132 288,178" fill="#ffffed" />
        </g>
    </svg>

    <svg id="hills" width="700" height="170">
        <polygon points="480,70 530,100 560,90 516,40" fill="#9b9d57" />
        <polygon points="480,70 530,100 412,84" fill="#7d8f57" />
        <polygon points="530,100 412,84 360,138" fill="#748857" />
        <polygon points="360,138 240,140 320,82" fill="#748857" />

        <polygon points="412,84 360,140 320,82" fill="#88945a" />
        <polygon points="320,82 240,140 210,64" fill="#597252" />
        <polygon points="300,78 100,100 0,104 170,58" fill="#4f654f" />
        <polygon points="172,58 145,40 122,48 66,79 0,104" fill="#536a50" />
    </svg>
  
    <svg height="347" width="168" id="cloud1">
        <g>
            <polygon points="0,30 8,19 27,18 22,36 9,37" fill="#d5d6e2" />
            <polygon points="0,30 9,37 3,50" fill="#c7c2d1" />
            <polygon points="3,50 9,37 22,36 33,44 14,55" fill="#a8a9b7" />
            <polygon points="14,55 33,44 36,52 23,58" fill="#7a7789" />
            <polygon points="27,18 22,36 33,44" fill="#acabb9" />

            <polygon points="31,11 51,4 66,1 83,13 83,23 78,23" fill="#fff6e7" />
            <polygon points="27,18 31,11 54,6 56,32 33,40 29,36" fill="#d0d0dc" />
            <polygon points="29,36 58,65 42,67 31,57" fill="#9694a3" />
            <polygon points="33,40 56,32 75,37 58,65" fill="#a2a1b1" />
            <polygon points="58,65 75,37 82,57" fill="#9897a7" />
            <polygon points="56,32 54,6 80,14 82,57 75,37" fill="#d7d6e2" />

            <polygon points="80,15 84,17 88,30 85,50 81,51" fill="#9d9da9" />
            <polygon points="90,16 82,20 81,31 95,35" fill="#cdcdda" />
            <polygon points="81,31 82,47 95,35" fill="#a2a2b0" />
            <polygon points="82,47 95,35 105,45 91,53" fill="#878892" />
            <polygon points="105,45 95,35 106,22" fill="#fbe5d5" />
            <polygon points="106,22 95,35 90,16" fill="#dbd6dd" />
        </g>
    </svg>

    <svg height="347" width="168" id="cloud2">
        <g transform="scale(0.5)">
            <polygon points="0,30 8,19 27,18 22,36 9,37" fill="#d5d6e2" />
            <polygon points="0,30 9,37 3,50" fill="#c7c2d1" />
            <polygon points="3,50 9,37 22,36 33,44 14,55" fill="#a8a9b7" />
            <polygon points="14,55 33,44 36,52 23,58" fill="#7a7789" />
            <polygon points="27,18 22,36 33,44" fill="#acabb9" />

            <polygon points="31,11 51,4 66,1 83,13 83,23 78,23" fill="#fff6e7" />
            <polygon points="27,18 31,11 54,6 56,32 33,40 29,36" fill="#d0d0dc" />
            <polygon points="29,36 58,65 42,67 31,57" fill="#9694a3" />
            <polygon points="33,40 56,32 75,37 58,65" fill="#a2a1b1" />
            <polygon points="58,65 75,37 82,57" fill="#9897a7" />
            <polygon points="56,32 54,6 80,14 82,57 75,37" fill="#d7d6e2" />

            <polygon points="80,15 84,17 88,30 85,50 81,51" fill="#9d9da9" />
            <polygon points="90,16 82,20 81,31 95,35" fill="#cdcdda" />
            <polygon points="81,31 82,47 95,35" fill="#a2a2b0" />
            <polygon points="82,47 95,35 105,45 91,53" fill="#878892" />
            <polygon points="105,45 95,35 106,22" fill="#fbe5d5" />
            <polygon points="106,22 95,35 90,16" fill="#dbd6dd" />
        </g>
    </svg>

    <svg id="ground"></svg>

    <svg class="trees">
        <g class="tree" id="tree" transform="translate(400,30)">
            <polygon points="25,75 27,44 21,34 25,33 30,41 38,33 40,34 31,46 29,75" fill="#3f2145" />
            <polygon points="29,75 31,46 32,45 32,74" fill="#812743" />

            <polygon points="2,21 11,33 20,32 27,29 32,23 24,35 11,34" fill="#282246" />
            <polygon points="27,29 33,13 18,0 29,2 37,13 32,23" fill="#6a7749" />

            <polygon points="33,23 35,32 45,37 55,27 44,35 37,31" fill="#210f3f" />
            <polygon points="37,31 38,17 46,17 50,31" fill="#354346" />
            <polygon points="37,31 50,31 45,37" fill="#292941" />
            <polygon points="33,23 37,31 38,17" fill="#2b2d42" />
            <polygon points="38,17 46,17 46,11" fill="#495e4b" />
            <polygon points="46,17 46,11 54,18" fill="#5b7049" />
            <polygon points="44,11 54,18 56,26 50,31" fill="#515d49" />

            <polygon points="11,33 20,32 27,29 15,19" fill="#292e42" />
            <polygon points="27,29 33,13 15,19" fill="#424f46" />
            <polygon points="33,13 18,0 15,19" fill="#48604a" />
            <polygon points="18,0 7,5 15,19" fill="#3a5449" />
            <polygon points="7,5 0,18 15,19" fill="#344847" />
            <polygon points="0,18 11,33 15,19" fill="#292c4b" />

            <polygon points="175,4 121,10 53,12 12,16 5,20 47,22 122,12 180,4" fill="#648155" transform="translate(-148,70)" />
        </g>

        <use x="-215" y="-23" xlink:href="#tree" transform="scale(0.8)" />
        <use x="-220" y="-20" xlink:href="#tree" />
        <use x="540" y="-30" xlink:href="#tree" />
        <use x="480" y="-20" xlink:href="#tree" />
        <use x="440" y="-15" xlink:href="#tree" transform="scale(1.2)" />

    </svg>

    <canvas id="sky"></canvas>


</section>
!

CSS 

              
                $darkblue: #0a1a27;
$lightblue: #4e83b7;
$greenprimary: #879759;
$greenshadow: #648459;

* { margin: 0; padding: 0; }

@media (max-width: 960px) {
  body { zoom: 0.7; }
}

html, body { height: 100%; }

@keyframes bounce {
  from {
    transform: translateY(0px);
  } to {
    transform: translateY(-4px);
  }
}

@keyframes sway-small {
  from {
    transform: translateX(0px);
  } to {
    transform: translateX(-24px);
  }
}

@keyframes sway-big {
  from {
    transform: translateX(0px);
  } to {
    transform: translateX(-48px);
  }
}

body {
    min-height: 100%;
    background: linear-gradient(40deg, #0a1a27, #4e83b7);
    position: relative;

    #mountains {
        z-index: 2;
        position: absolute;
        bottom: 20%;
        margin-bottom: -16px;
        left: 100px;
    }
  
    #hills {
        // background: rgba(255,0,0,0.3);
        position: absolute;
        left: 100px;
        margin-left: -120px;
        margin-bottom: -86px;
        bottom: 20%;
        z-index: 3;
    }

    #cloud1 {
        z-index: 2;
        position: absolute;
        top: 20%;
        right: 4%;
        animation: sway-big 10s ease-in-out 0s infinite alternate;
    }

    #cloud2 {
        z-index: 1;
        position: absolute;
        top: 22%;
        right: 16%;
        animation: sway-small 10s ease-in-out 0s infinite alternate;
    }

    .trees {
        width: 100%;
        height: 130px;
        z-index: 4;
        position: absolute;
        bottom: 20%;
        margin-bottom: -100px;
    }

    #ground {
        z-index: 1;
        width: 100%;
        height: 20%;
        position: absolute;
        bottom: 0;
        background: $greenprimary;
        background: linear-gradient(210deg, $greenprimary, $greenshadow);
    }

    #stars {
        width: 100%;
        height: 100%;
    }
}
!

JS 

              
                var sky = document.getElementById("sky");

sky.width = document.body.clientWidth;
sky.height = document.body.clientHeight;

if (sky.getContext){
    var skyContext = sky.getContext("2d");

    var radius = 2;

    for(var star = 0; star < 240; star++){ 
        var min = ( Math.random() * 30 ) / 10;
        var max = sky.width - radius;

        var centerX = Math.floor(Math.random() * (max - min + 1)) + min;
        var centerY = Math.floor(Math.random() * (max - min + 1)) + min;

        skyContext.beginPath();
        skyContext.arc(centerX, centerY, min, 0, 2 * Math.PI);

        console.log(min);
        var opacity = Math.random();
      
        skyContext.fillStyle = "rgba(255, 255, 255, " + opacity + ")";
        skyContext.fill();
    }
}
!
999px

Console