CSS Style to Submit Button

Hi, i would like to assign a css class to the submit button, the code is the following:

.art-button-wrapper .art-button
{
  font-family: Calibri,Arial, Helvetica, Sans-Serif;
  font-style: normal;
  font-weight: bold;
  font-size: 12px;
  display: inline-block;
  vertical-align: middle;
  white-space: nowrap;
  text-align: left;
  text-decoration: none !important;
  color: #E7E9E7 !important;
  width: auto;
  outline: none;
  border: none;
  background: none;
  line-height: 33px;
  height: 33px;
  margin: 0 !important;
  padding: 0 21px !important;
  overflow: visible;
  cursor: default;
  z-index: 0;
}

.art-button img, .art-button-wrapper img
{
  margin: 0;
  vertical-align: middle;
}

.art-button-wrapper
{
  vertical-align: middle;
  display: inline-block;
  position: relative;
  height: 33px;
  overflow: hidden;
  white-space: nowrap;
  width: auto;
  margin: 0;
  padding: 0;
  z-index: 0;
}

.firefox2 .art-button-wrapper
{
  display: block;
  float: left;
}

input, select, textarea, select
{
  vertical-align: middle;
  font-family: Calibri,Arial, Helvetica, Sans-Serif;
  font-style: normal;
  font-weight: bold;
  font-size: 12px;
}

.art-block select
{
    width:96%;
}

.art-button-wrapper.hover .art-button, .art-button:hover
{
  color: #E7E9E7 !important;
  text-decoration: none !important;
}

.art-button-wrapper.active .art-button
{
  color: #E7E9E7 !important;
}

.art-button-wrapper .l, .art-button-wrapper .r
{
  display: block;
  position: absolute;
  z-index: -1;
  height: 99px;
  margin: 0;
  padding: 0;
  background-image: url('button.png');
}

.art-button-wrapper .l
{
  left: 0;
  right: 10px;
}

.art-button-wrapper .r
{
  width: 409px;
  right: 0;
  clip: rect(auto, auto, auto, 399px);
}

.art-button-wrapper.hover .l, .art-button-wrapper.hover .r
{
  top: -33px;
}

.art-button-wrapper.active .l, .art-button-wrapper.active .r
{
  top: -66px;
}

.art-button-wrapper input
{
  float: none !important;
}

How can i doing? Someone maybe can help me please?
Greets ??

https://www.ads-software.com/extend/plugins/si-contact-form/