c3/src/scss/arc.scss

.c3-chart-arcs-title {
  dominant-baseline: middle;
  font-size: 1.3em;
}

.c3-chart-arcs .c3-chart-arcs-background {
  fill: #e0e0e0;
  stroke: none;
}
.c3-chart-arcs .c3-chart-arcs-gauge-unit {
  fill: #000;
  font-size: 16px;
}
.c3-chart-arcs .c3-chart-arcs-gauge-max {
  fill: #777;
}
.c3-chart-arcs .c3-chart-arcs-gauge-min {
  fill: #777;
}

.c3-chart-arc .c3-gauge-value {
  fill: #000;
/*  font-size: 28px !important;*/
}

.c3-chart-arc.c3-target g path {
  opacity: 1;
}

.c3-chart-arc.c3-target.c3-focused g path {
  opacity: 1;
}