my-custom-styles.html

<style is="custom-style">
  iron-icon{
    color: white;
  }
  .header_icon{
    color: white;
  }
  paper-ripple{
    color: #03a9f4;
  }
  paper-button{
    background-color: white;
    color: #0b3f5c;
  }
  #myButton{
    background: #ff5252;
    color: white;
  }
  paper-card{
    background: #0288d1;
  }
  h1{
    font-size: 30px;
  }
  paper-progress{
    --paper-progress-active-color: #ff5252;
  }

</style>