Create Color Constants and Replace Old Styles with Them

[lindsayJohnstonPnnl]

We don't have any style constants defined in our App.css stylesheet. We should create color constants according to Teressa's style guide and replace all instances of style definitions with these constants.

It would look something like this:

:root {
  --primary-color: #4CAF50;
  --secondary-color: #FF9800;
  --background-color: #F0F0F0;
  --text-color: #333333;
}

body {
  background-color: var(--background-color);
  color: var(--text-color);
}

button {
  background-color: var(--primary-color);
  color: var(--background-color);
  border: none;
  padding: 10px 15px;
  cursor: pointer;
}