posts.scss

...
.solid-color-mode, .border-color-mode {
  .post-text {
    text-align: center;
  }
}

.solid-color-mode {
  .post-text {
    padding: 10px;
    background-color: white;
    border-radius: 25px;
  }
}

.border-color-mode {
  background-color: white;
}