Page styling - https://solusipress.com/kirim-pesan-ke-whatsapp-dengan-salam-pembuka-dinamis/

contact-form-wa.css

.sp-form-contact input,
.sp-form-contact button { 
  width: 100%; 
  padding: 10px;
}
.sp-form-contact button {
  cursor: pointer;
  border: 1px solid #666;
  border-radius: 5px;
  box-shadow: none;
  -webkit-box-shadow: none;
}

/**
*** SIMPLE GRID
*** (C) ZACH COLE 2016
*** https://github.com/zachacole/Simple-Grid/blob/master/simple-grid.css
*** modified by SolusiPress
**//* ==== GRID SYSTEM ==== */
.container {
  width: 90%;
  margin-left: auto;
  margin-right: auto;
}

.row {
  position: relative;
  width: 100%;
}

.row [class^="col"] {
  float: left;
  margin: 0.5rem 2%;
  min-height: 0.125rem;
}

.col-1,
.col-2,
.col-3,
.col-4,
.col-5,
.col-6,
.col-7,
.col-8,
.col-9,
.col-10,
.col-11,
.col-12 {
  width: 96%;
}

.col-1-sm {
  width: 4.33%;
}

.col-2-sm {
  width: 12.66%;
}

.col-3-sm {
  width: 21%;
}

.col-4-sm {
  width: 29.33%;
}

.col-5-sm {
  width: 37.66%;
}

.col-6-sm {
  width: 46%;
}

.col-7-sm {
  width: 54.33%;
}

.col-8-sm {
  width: 62.66%;
}

.col-9-sm {
  width: 71%;
}

.col-10-sm {
  width: 79.33%;
}

.col-11-sm {
  width: 87.66%;
}

.col-12-sm {
  width: 96%;
}

.row::after {
content: "";
display: table;
clear: both;
}

.hidden-sm {
  display: none;
}

@media only screen and (min-width: 33.75em) {  /* 540px */  .container {
    width: 80%;
  }
}

@media only screen and (min-width: 45em) {  /* 720px */  .col-1 {
    width: 4.33%;
  }

  .col-2 {
    width: 12.66%;
  }

  .col-3 {
    width: 21%;
  }

  .col-4 {
    width: 29.33%;
  }

  .col-5 {
    width: 37.66%;
  }

  .col-6 {
    width: 46%;
  }

  .col-7 {
    width: 54.33%;
  }

  .col-8 {
    width: 62.66%;
  }

  .col-9 {
    width: 71%;
  }

  .col-10 {
    width: 79.33%;
  }

  .col-11 {
    width: 87.66%;
  }

  .col-12 {
    width: 96%;
  }

  .hidden-sm {
    display: block;
  }
}

@media only screen and (min-width: 60em) { /* 960px */  .container {
    width: 100%;
    max-width: 90rem;
  }
}