index.css

/* Example of adjusting UI styles to the user's current color theme using ThemeParams */
:root {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen',
    'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue',
    sans-serif;

  color: var(--tg-theme-text-color);
  background-color: var(--tg-theme-bg-color);

  font-synthesis: none;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  -webkit-text-size-adjust: 100%;
}

code {
  font-family: source-code-pro, Menlo, Monaco, Consolas, 'Courier New',
    monospace;
}

html,
body,
#root {
  width: 100%;
  height: 100%;
  margin: 0;
}

#root {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
}

/* Example of adjusting UI styles to the user's current color theme using ThemeParams */
button {
  cursor: pointer;
  border-radius: 8px;
  padding: 10px 25px;
  background-color: var(--tg-theme-button-color);
  color: var(--tg-theme-button-text-color);
  user-select: none;
  border: none;
  font-family: inherit;
  font-size: inherit;
}