To style a form, there are various of properties for styling.

Ex:

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen,    Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
  line-height: 1.5;
  padding: 1rem;
}
label {
  display: block;
}

input[type="text"],
input[type="email"] {
  border: 1px solid #ccc;
  border-radius: 5px;
  padding: 0.5rem 0.7rem;
  /* color transform when switching boxes */
  transition: border-color 0.15s, box-shadow 0.15s;
}

/* when input box is selected */
input[type="text"]:focus,
input[type="email"]:focus {
  border-color: #7db0fb;
  /* get rid of system default outline */
  outline: 0;
  box-shadow: 0 0 0 4px rgba(24, 117, 255, 0.25);
}

button {
  background-color: #0d6efd;
  color: white;
  border: 0;
  padding: 0.5rem 0.7rem;
  border-radius: 5px;
  outline: 0;
}

.form-group {
  margin-bottom: 1rem;
}