Changing Vuetify's Button Width And Padding

The issue is the min-width of the .btn class. Setting that to 0 will allow the button to be smaller than 88px. You should also just set the padding of the .btn__content to 0.

div.btn__content {
  padding: 0;
}

div.card__actions .btn {
  min-width: 0;
}

Here's an updated codepen.

For newer versions of Vuetify (1.2.4 and above) you need to use this:

/* turn off min-width for all buttons */
.v-btn {
  min-width: 0;
}