html, body {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
  overflow: hidden;
  background: rgb(1,1,1);
  color: white;
  font-family: Arial, "Microsoft YaHei", sans-serif;
}
.screen {
  width: 100vw;
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgb(1,1,1);
}
.content {
  width: 90vw;
  max-width: 1100px;
  min-height: 50vh;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  white-space: pre-line;
  font-size: 4.8vh;
  line-height: 1.55;
}
.fixation {
  font-size: 12vh;
  color: red;
  line-height: 1;
}
.target {
  width: min(30vh, 30vw);
  height: min(30vh, 30vw);
  border-radius: 50%;
  border: 1px solid rgb(1,1,1);
}
.small-note {
  font-size: 2.4vh;
  line-height: 1.4;
  opacity: 0.9;
  margin-top: 2vh;
}
button {
  font-size: 2.4vh;
  padding: 0.8em 1.2em;
  border-radius: 0.4em;
  border: 1px solid #888;
  cursor: pointer;
}