/* === RESPONSIVE === */
            @media (max-width: 1200px) {
                .shell {
                    grid-template-columns: 280px minmax(0, 1fr) 280px;
                }
            }

            @media (max-width: 900px) {
                .shell {
                    grid-template-columns: 1fr;
                    grid-template-rows: auto minmax(300px, 1fr) auto;
                    overflow-y: auto;
                }

                .panel-left, .panel-right {
                    height: auto;
                    max-height: none;
                    border: none;
                    border-bottom: 1px solid var(--border);
                }

                .stage { min-height: 50vh; order: 0; }
                .panel-left { order: 1; }
                .panel-right { order: 2; }

                .mask-wrap { width: 100%; }
                .mask-wrap.is-expanded { width: min(1000px, calc(100vw - 24px)); }
            }

            @media (max-width: 640px) {
                .site-topbar { grid-template-columns: 1fr auto; gap: 8px; padding: 0 8px; }
                .site-brand-text { font-size: 15px; }
                .site-page-title { display: none; }
                .site-status-pill { display: none; }

                .mask-floating-toolbar {
                    bottom: 4px;
                    width: calc(100vw - 8px);
                    gap: 2px;
                    padding: 3px;
                }
                .float-tool-button { min-width: 28px; min-height: 28px; padding: 3px 5px; }
                .float-tool-divider { display: none; }
                .float-transform-readout { min-width: 52px; }
                .float-tool-context { flex-wrap: wrap; justify-content: center; }

                .pivot-download { grid-template-columns: 28px minmax(0, 1fr); }
                .pivot-mark { width: 28px; height: 28px; }
                .pivot-link { grid-column: 2; justify-self: start; }
            }

            @media (prefers-reduced-motion: reduce) {
                *, *::before, *::after {
                    scroll-behavior: auto !important;
                    transition: none !important;
                    animation-duration: 0.01ms !important;
                }
            }