message: add variable css to template
diff: <!-- HTTP_STYLE -->
  <style>
  +:root{
  + /* CSS VARIABLE THEME COLOR */
  + /*--primarycolor:#9933CC;*/
  + --primarycolor:#1fa3ec;
  +}
  +
  body.invert,
  body.invert a,
  body.invert h1 {
  @@ -50,13 +56,13 @@ input,button,.msg{
  }
  button,input[type="button"],input[type="submit"] {
  border: 0;
  - background-color: #9933CC;
  + background-color: var(--primarycolor);
  color: #fff;
  line-height: 2.4rem;
  font-size: 1.2rem;
  }
  input[type="file"]{
  - border: 1px solid #9933CC;
  + border: 1px solid var(--primarycolor);
  }
  a {
  color: #000;
  @@ -64,7 +70,7 @@ a {
  text-decoration: none;
  }
  a:hover {
  - color: #9933CC;
  + color: var(--primarycolor);
  text-decoration: underline;
  }
  .h {
  @@ -128,10 +134,10 @@ a:hover {
  margin-bottom: 5px;
  }
  .msg.P {
  - border-left-color: #9933CC;
  + border-left-color: var(--primarycolor);
  }
  .msg.P h4 {
  - color: #9933CC;
  + color: var(--primarycolor);
  }
  /*.msg.S {
  border-left-color: #5cb85c;
  @@ -297,7 +303,7 @@ button.D{
  <p/>More information about WiFiManager at <a href='https://github.com/tzapu/WiFiManager'>https://github.com/tzapu/WiFiManager</a>
  <!-- /HTTP_HELP -->
  <!-- FORM_UPLOAD -->
  - <Br/><br/>Form UPLOAD<br/><form method='POST' action='u' enctype='multipart/form-data'><input type='file' name='update' accept='.bin,application/octet-stream'><input type='submit' value='Submit'></form>
  + <Br/><br/>Form UPLOAD<br/><form method='POST' action='u' enctype='multipart/form-data'><input type='file' name='update' accept='.bin,application/octet-stream'><button type='submit' value='Submit'>Submit</button></form>
  <!-- /FORM_UPLOAD -->
  <!-- HTTP_END -->
  