The following custom CSS is used on both todon.eu and todon.nl.

/* Wide screen advanced UI */

@media (min-width: 701px) {

div.column {
        flex-grow: 1 !important;
}

.drawer__inner__mastodon {
	background: none;
}

}

/* Toot button */

.ui__header__links > .button[href="/publish"], .compose-form__publish-button-wrapper > .button.button--block {
  font-size: 0 !important;
}

.ui__header__links > .button[href="/publish"]::after, .compose-form__publish-button-wrapper > .button.button--block::after {
  content: "Toot!";
  text-transform: none;
  font-size: 15px;
  position: relative;
  bottom: -2px;
}

/* Boost icon */

div.notification.notification-reblog.focusable div.notification__message div.notification__favourite-icon-wrapper i.fa.fa-retweet.fa-fw, button.status__action-bar__button.icon-button.active.icon-button--with-counter span.icon-button__counter {
  color: #19A341;
}

button.status__action-bar__button.star-icon.icon-button.active.icon-button--with-counter span.icon-button__counter span.animated-number span span {
  color: #ca8f04 !important;
}

In the code itself I changed the files app/javascript/styles/mastodon/boost.scss and app/javascript/styles/mastodon/variables.scss to make sure boosted posts are #19A341.