Particle JS - Covering the full page

particlesJS("particles-js", {
  "particles": {
    "number": {
      "value": 355,
      "density": {
        "enable": true,
        "value_area": 789.1476416322727
      }
    },
    "color": {
      "value": "#ffffff"
    },
    "shape": {
      "type": "circle",
      "stroke": {
        "width": 0,
        "color": "#000000"
      },
      "polygon": {
        "nb_sides": 5
      },
      "image": {
        "src": "img/github.svg",
        "width": 100,
        "height": 100
      }
    },
    "opacity": {
      "value": 0.48927153781200905,
      "random": false,
      "anim": {
        "enable": true,
        "speed": 0.2,
        "opacity_min": 0,
        "sync": false
      }
    },
    "size": {
      "value": 2,
      "random": true,
      "anim": {
        "enable": true,
        "speed": 2,
        "size_min": 0,
        "sync": false
      }
    },
    "line_linked": {
      "enable": false,
      "distance": 150,
      "color": "#ffffff",
      "opacity": 0.4,
      "width": 1
    },
    "move": {
      "enable": true,
      "speed": 0.2,
      "direction": "none",
      "random": true,
      "straight": false,
      "out_mode": "out",
      "bounce": false,
      "attract": {
        "enable": false,
        "rotateX": 600,
        "rotateY": 1200
      }
    }
  },
  "interactivity": {
    "detect_on": "canvas",
    "events": {
      "onhover": {
        "enable": true,
        "mode": "bubble"
      },
      "onclick": {
        "enable": true,
        "mode": "push"
      },
      "resize": true
    },
    "modes": {
      "grab": {
        "distance": 400,
        "line_linked": {
          "opacity": 1
        }
      },
      "bubble": {
        "distance": 83.91608391608392,
        "size": 1,
        "duration": 3,
        "opacity": 1,
        "speed": 3
      },
      "repulse": {
        "distance": 200,
        "duration": 0.4
      },
      "push": {
        "particles_nb": 4
      },
      "remove": {
        "particles_nb": 2
      }
    }
  },
  "retina_detect": true
});

html,
body {
    margin: 0;
    padding: 0;
    height: 100vh;
    width: 100%;
    overflow-x: hidden;
}

header {
    width: 100%;
    height: 100vh;
    margin: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    color: white;
    background-size: cover;
}

#particles-js canvas {
    height: 100vh;
    position: absolute;
    top: 0;
    left: 0;
    z-index: -1;
    background-color: black;
    background-size: cover;
}


.container {
    flex-wrap: wrap;
}

h1 {
    width: 100%;
    font-family: 'Montserrat', sans-serif;
    font-weight: 900;
    font-size: 72px;
}

h2 {
    font-family: 'Montserrat', sans-serif;
    font-weight: 300;
    font-size: 24px;
}

.btn-primary {
    font-size: 1.25rem;
    font-family: 'Montserrat', sans-serif;
    font-weight: 400;
    display: inline-block;
    padding: 0.5em 1em;
    margin-top: 1em;
    color: #EB429C;
    background-color: transparent;
    border: #EB429C 0.125em solid;
    cursor: pointer;
    text-shadow: 0 0 0.125em hsl(0 0% 100% / 0.3), 0 0 0.45em currentColor;
    box-shadow: inset 0 0 0.5em 0 #EB429C, 0 0 0.5em 0 #EB429C;
    position: relative;
    transition: background-color 100ms linear;
}

.btn-primary::before {
    pointer-events: none;
    content: '';
    position: absolute;
    background: #EB429C;
    top: 120%;
    left: 0;
    width: 100%;
    height: 100%;

    transform: perspective(1em) rotateX(40deg) scale(1, 0.35);
    filter: blur(1.5em);
    opacity: 0.25;

}

.btn-primary::after {
    content: '';
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    box-shadow: 0 0 1em 0.5em #EB429C;
    opacity: 0;
    transition: opacity 100ms linear;
}

.btn-primary:hover,
.btn-primary:focus {
    color: black;
    background-color: #EB429C;
    border: #EB429C 0.125em solid;
    text-shadow: none;
}

.btn-primary:hover::before {
    opacity: 1;
}

.btn-primary:hover::after {
    opacity: 1;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/particles.js/2.0.0/particles.min.js"></script>
<header>
  <div id="particles-js">
    <div class="container">
      <h1> Test Bed </h1>
      <h2>Sub text to go here</h2>
      <button class="btn-primary"> CONTACT US </button>
    </div>
  </div>
</header>

<div class="container">
  <h1>Hello there</h1>
</div>