/* 仅供开篇使用，沿用课程投影字体和导航。 */
.canvas-showcase {
  display: grid;
  grid-template-columns: 1.25fr 1fr;
  gap: 24px;
  color: #17344a;
  font-family: "Microsoft YaHei", sans-serif;
}
.canvas-showcase article {
  min-width: 0;
  padding: 16px;
  border: 1px solid #cbd8dd;
  border-radius: 12px;
  background: #fff;
}
.canvas-showcase h3 { margin: 0 0 12px; font-size: 24px; }
.canvas-showcase h3 small { display: block; margin-top: 5px; color: #a63832; font-size: 18px; }
.canvas-showcase canvas { display: block; width: 100%; height: auto; border-radius: 6px; }
.canvas-showcase p { margin: 10px 0 0; font-size: 20px; line-height: 1.5; }
.canvas-extras { display: grid; gap: 16px; min-width: 0; }
.canvas-actions { display: flex; align-items: center; flex-wrap: wrap; gap: 12px; margin-top: 12px; font-size: 18px; }
.canvas-actions button { padding: 8px 16px; color: #fff; background: #17344a; border: 2px solid #17344a; border-radius: 6px; font: inherit; cursor: pointer; }
.canvas-actions button:hover { background: #28556d; }
.canvas-actions button:focus-visible { outline: 3px solid #a63832; outline-offset: 3px; }
@media (max-width: 820px) {
  .canvas-showcase { grid-template-columns: 1fr; }
}