mermaid/src/less/forest/sequenceDiagram.less

.actor {
  stroke: @actorBorder;
  fill: @actorBkg;
}

text.actor {
  fill: @actorTextColor;
  stroke: none;
}

.actor-line {
  stroke: @actorLineColor;
}

.messageLine0 {
  stroke-width: 1.5;
  stroke-dasharray: "2 2";
  marker-end: "url(#arrowhead)";
  stroke: @signalColor;
}

.messageLine1 {
  stroke-width: 1.5;
  stroke-dasharray: "2 2";
  stroke: @signalColor;
}

#arrowhead {
  fill: @signalColor;
}

#crosshead path {
  fill: @signalColor !important;
  stroke: @signalColor !important;
}

.messageText {
  fill: @signalTextColor;
  stroke: none;
}

.labelBox {
  stroke: @labelBoxBorderColor;
  fill: @labelBoxBkgColor;
}

.labelText {
  fill: @labelTextColor;
  stroke: none;
}

.loopText {
  fill: @labelTextColor;
  stroke: none;
}

.loopLine {
  stroke-width: 2;
  stroke-dasharray: "2 2";
  marker-end: "url(#arrowhead)";
  stroke: @labelBoxBorderColor;
}

.note {
  //stroke: #decc93;
  stroke: @noteBorderColor;
  fill: @noteBkgColor;
}

.noteText {
  fill: black;
  stroke: none;
  font-family: 'trebuchet ms', verdana, arial;
  font-size: 14px;
}