:root{--bg:#f5f6f8;--surface:#fff;--border:#d9dce1;--text:#1c1f24;--text-muted:#6b7280;--accent:#2f6feb;--accent-2:#d2691e;--accent-contrast:#fff;--error-bg:#fdeceb;--error-border:#e5534b;--error-text:#8a1f16;--correct:#1a7f37;--wrong:#d1242f;--sans:system-ui, "Segoe UI", Roboto, sans-serif;--mono:ui-monospace, Consolas, monospace;--lightningcss-light:initial;--lightningcss-dark: ;color-scheme:light}:root[data-theme=dark]{--bg:#14161a;--surface:#1b1e24;--border:#2e333c;--text:#e6e8eb;--text-muted:#9aa1ac;--accent:#5b9dff;--accent-2:#ffa057;--accent-contrast:#0b1220;--error-bg:#3a1c1c;--error-border:#e5534b;--error-text:#ffb4ac;--correct:#4ac26b;--wrong:#ff7b72;--lightningcss-light: ;--lightningcss-dark:initial;color-scheme:dark}body{font:16px/1.5 var(--sans);background:var(--bg);color:var(--text);margin:0}.app{max-width:1100px;margin:0 auto;padding:16px 20px 48px}.site-header{align-items:center;gap:10px;margin-bottom:20px;display:flex}.site-header__brand{color:var(--accent);white-space:nowrap;font-size:15px;font-weight:700;text-decoration:none}.site-header__brand:hover{text-decoration:underline}.site-header__divider{color:var(--text-muted);font-weight:400}.site-header__title{color:var(--text-muted);white-space:nowrap;font-size:15px;font-weight:600}.toolbar-spacer{flex:1}.btn,.toggle-btn{border:1px solid var(--border);background:var(--surface);color:var(--text);cursor:pointer;border-radius:6px;padding:6px 12px;font-size:13px}.btn:hover,.toggle-btn:hover{border-color:var(--accent)}.icon-btn{padding:6px 10px}.btn--active{border-color:var(--accent);color:var(--accent);font-weight:600}.nav-tabs{border-bottom:1px solid var(--border);gap:4px;margin-bottom:20px;display:flex}.nav-tabs__tab{color:var(--text-muted);border-bottom:2px solid #0000;padding:8px 16px;font-size:14px;font-weight:600;text-decoration:none}.nav-tabs__tab:hover{color:var(--text)}.nav-tabs__tab--active{color:var(--accent);border-bottom-color:var(--accent)}.app__main{min-height:400px}.split-layout{grid-template-columns:240px 1fr;align-items:start;gap:24px;display:grid}@media (width<=720px){.split-layout{grid-template-columns:1fr}}.side-list{border:1px solid var(--border);background:var(--surface);border-radius:8px;flex-direction:column;gap:2px;display:flex;overflow:hidden}.side-list__item{color:var(--text);border-left:3px solid #0000;align-items:center;gap:8px;padding:8px 10px;font-size:13px;text-decoration:none;display:flex}.side-list__item:hover{background:var(--bg)}.side-list__item--active{border-left-color:var(--accent);background:var(--bg);font-weight:600}.side-list__label{flex:1}.concept-view{background:var(--surface);border:1px solid var(--border);border-radius:8px;margin:16px 0;padding:20px 24px}.concept-view__header{flex-wrap:wrap;justify-content:space-between;align-items:center;gap:12px;display:flex}.concept-view__header h3{margin:0}.concept-view h3{margin-top:0}.chip-row{flex-wrap:wrap;align-items:center;gap:6px;margin-top:16px;display:flex}.chip-row__label{color:var(--text-muted);margin-right:4px;font-size:13px}.chip{border:1px solid var(--border);background:var(--bg);color:var(--text);border-radius:999px;padding:3px 10px;font-size:12px;text-decoration:none;display:inline-block}.chip:hover,.chip--link{border-color:var(--accent);color:var(--accent)}.chip--filter{cursor:pointer;font:inherit}.chip--filter-active{border-color:var(--accent);color:var(--accent);background:var(--bg);font-weight:600}.empty-state{color:var(--text-muted);font-style:italic}.tool-panel{max-width:640px}.tool-panel__hint{color:var(--text-muted);margin-top:0;font-size:13px}.tool-panel__error{color:var(--wrong);margin-top:10px;font-size:13px}.tool-input-label{color:var(--text-muted);margin:12px 0 4px;font-size:12px;display:block}.tool-input{box-sizing:border-box;border:1px solid var(--border);background:var(--surface);width:100%;color:var(--text);font-family:var(--mono);border-radius:6px;padding:8px 10px;font-size:14px}.tool-input:focus{border-color:var(--accent);outline:none}.tool-format-toggle{gap:8px;margin-top:12px;display:flex}.results-table{border-collapse:collapse;width:100%;margin-top:16px;font-size:13px}.results-table th,.results-table td{border:1px solid var(--border);text-align:left;padding:6px 10px}.results-table th{background:var(--bg);white-space:nowrap;width:40%}.results-table__mono{font-family:var(--mono)}.results-table--breakdown th,.results-table--breakdown td{text-align:center;width:auto}.results-table--ports th{width:auto}.quiz-mode-toggle{gap:8px;margin-bottom:16px;display:flex}.quiz-controls{color:var(--text-muted);flex-wrap:wrap;align-items:center;gap:14px;margin-bottom:12px;font-size:13px;display:flex}.quiz-controls__progress{color:var(--text);font-weight:600}.mcq-question{background:var(--surface);border:1px solid var(--border);border-radius:8px;max-width:560px;padding:20px 24px}.mcq-question__prompt{font-size:16px;font-weight:600}.mcq-question__choices{flex-direction:column;gap:8px;margin:0;padding:0;list-style:none;display:flex}.mcq-choice{text-align:left;border:1px solid var(--border);background:var(--bg);width:100%;color:var(--text);cursor:pointer;border-radius:6px;padding:10px 12px;font-size:14px}.mcq-choice:hover:not(:disabled){border-color:var(--accent)}.mcq-choice:disabled{cursor:default}.mcq-choice--correct{border-color:var(--correct);color:var(--correct);font-weight:600}.mcq-choice--wrong{border-color:var(--wrong);color:var(--wrong)}.mcq-question__feedback{border-top:1px solid var(--border);flex-direction:column;align-items:flex-start;gap:10px;margin-top:16px;padding-top:16px;display:flex}.flashcard{max-width:480px}.flashcard__card{border:1px solid var(--border);background:var(--surface);width:100%;min-height:160px;color:var(--text);cursor:pointer;text-align:center;border-radius:10px;justify-content:center;align-items:center;padding:24px;font-size:16px;display:flex}.flashcard__front{font-weight:600}.flashcard__back p{margin:8px 0}.flashcard__explanation{color:var(--text-muted);font-size:14px}.flashcard__controls{flex-wrap:wrap;align-items:center;gap:10px;margin-top:12px;display:flex}.flashcard__hint{color:var(--text-muted);margin-top:8px;font-size:13px}.score-summary{background:var(--surface);border:1px solid var(--border);border-radius:8px;max-width:480px;padding:24px}.score-summary__actions{gap:10px;margin-top:12px;display:flex}.visualizer-view{min-width:0}.step-controls{align-items:center;gap:12px;margin-top:16px;display:flex}.step-controls__dots{gap:6px;display:flex}.step-controls__dot{border:1px solid var(--border);background:var(--surface);cursor:pointer;border-radius:50%;width:10px;height:10px;padding:0}.step-controls__dot--active{background:var(--accent);border-color:var(--accent)}.osi-stack{flex-direction:column;gap:4px;max-width:460px;display:flex}.osi-layer{border:1px solid var(--border);background:var(--surface);color:var(--text);cursor:pointer;text-align:left;border-radius:6px;align-items:center;gap:10px;padding:10px 14px;font-size:14px;display:flex}.osi-layer:hover{border-color:var(--accent)}.osi-layer--active{border-color:var(--accent);background:var(--bg);font-weight:600}.osi-layer__number{background:var(--bg);width:22px;height:22px;color:var(--text-muted);border-radius:50%;flex:none;justify-content:center;align-items:center;font-size:12px;display:inline-flex}.osi-layer--active .osi-layer__number{background:var(--accent);color:var(--accent-contrast)}.encap-stage{justify-content:center;align-items:center;min-height:220px;padding:24px;display:flex}.encap-box{border:2px solid var(--accent);background:color-mix(in srgb, var(--accent) 8%, var(--surface));border-radius:10px;flex-direction:column;align-items:center;gap:10px;padding:14px;display:flex}.encap-box__header-label{color:var(--accent);text-transform:uppercase;letter-spacing:.03em;align-self:flex-start;font-size:11px;font-weight:600}.encap-box__core{border:2px dashed var(--border);background:var(--surface);border-radius:6px;padding:18px 28px;font-weight:600}.handshake-diagram{grid-template-columns:120px 1fr 120px;align-items:stretch;gap:12px;margin:16px 0;display:grid}@media (width<=560px){.handshake-diagram{grid-template-columns:1fr}}.handshake-column{border:1px solid var(--border);background:var(--surface);text-align:center;border-radius:8px;flex-direction:column;justify-content:center;align-items:center;gap:6px;padding:12px;display:flex}.handshake-column__label{font-weight:600}.handshake-column__state{font-family:var(--mono);color:var(--accent);font-size:12px}.handshake-arrows{flex-direction:column;justify-content:center;gap:10px;min-height:100px;display:flex}.handshake-arrow{align-items:center;gap:8px;font-size:13px;display:flex}.handshake-arrow--server{flex-direction:row-reverse}.handshake-arrow__line{color:var(--text-muted);font-size:16px}.handshake-arrow__label{font-family:var(--mono);background:var(--bg);border:1px solid var(--border);border-radius:4px;padding:3px 8px;font-size:12px}.handshake-arrow--current .handshake-arrow__label{border-color:var(--accent);color:var(--accent);font-weight:600}.handshake-arrow--current .handshake-arrow__line{color:var(--accent)}.dns-chain{flex-wrap:wrap;align-items:center;gap:8px;margin:16px 0;display:flex}.dns-node{border:1px solid var(--border);background:var(--surface);color:var(--text-muted);border-radius:999px;padding:6px 14px;font-size:12px}.dns-node--visited{border-color:var(--correct);color:var(--correct)}.dns-node--active{border-color:var(--accent);color:var(--accent);background:var(--bg);font-weight:600}.dns-chain__sep{color:var(--text-muted)}