/* C++ 100 Drills — a quiet, paper-like learning workspace. */
:root{
  color-scheme:light;
  --bg:#fdfdfb;--sidebar:#f5f6f2;--panel:#fff;--panel2:#f1f3ee;
  --line:#e0e4dc;--text:#202923;--muted:#626e64;--subtle:#697366;
  --accent:#38644b;--accent-soft:#e6eee4;--accent2:#526b80;--danger:#a04b43;
  --code:#f2f4ef;--topbar:rgba(253,253,251,.95);--shadow:rgba(27,44,31,.1);
  --max:1020px;--side-width:282px;
  --sans:-apple-system,BlinkMacSystemFont,"Segoe UI","Apple SD Gothic Neo","Noto Sans KR",sans-serif;
  --mono:"SFMono-Regular",Consolas,"Liberation Mono",monospace;
  font-family:var(--sans);
}
html[data-theme="dark"]{
  color-scheme:dark;--bg:#191e1b;--sidebar:#151a17;--panel:#1e2520;--panel2:#242e27;
  --line:#354137;--text:#edf0e9;--muted:#b2bcae;--subtle:#98a793;
  --accent:#b5d0b1;--accent-soft:#2c3e30;--accent2:#b0c2d2;--danger:#e3a199;
  --code:#151c17;--topbar:rgba(25,30,27,.96);--shadow:rgba(0,0,0,.2);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth;scroll-padding-top:100px;-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--text);font-size:15px;line-height:1.8;-webkit-font-smoothing:antialiased}
button,input,select{font:inherit}button{cursor:pointer}a{color:inherit;text-decoration:none}
button,a,input,select,summary{-webkit-tap-highlight-color:transparent}
button:disabled{opacity:.35;cursor:default;transform:none!important}
:focus-visible{outline:2px solid var(--accent);outline-offset:4px}
::selection{background:var(--accent-soft);color:var(--text)}
.skip-link{position:fixed;left:16px;top:-70px;z-index:50;background:var(--text);color:var(--bg);padding:9px 16px;border-radius:4px}.skip-link:focus{top:14px}
.app-shell{min-height:100vh}
.sidebar{position:fixed;inset:0 auto 0 0;width:var(--side-width);background:var(--sidebar);border-right:1px solid var(--line);padding:30px 20px 18px;display:flex;flex-direction:column;z-index:20}
.brand{display:flex;align-items:center;gap:12px;padding:0 4px 29px;min-height:74px}
.brand-mark{width:42px;height:42px;display:inline-flex;align-items:center;justify-content:center;flex-shrink:0;border:1px solid var(--line);border-radius:8px;font-family:var(--mono);font-size:18px;font-weight:600;letter-spacing:-1.5px;background:var(--bg);line-height:1}
.brand-mark span{color:var(--accent);font-size:17px}
.brand strong{display:block;font-size:12px;font-weight:650;letter-spacing:.17em;line-height:1.5}
.brand small{display:block;color:var(--muted);font-size:9px;letter-spacing:.025em;margin-top:4px;white-space:nowrap}
.brand .icon-btn{margin-left:auto}
.side-progress{padding:0 5px 23px;margin-bottom:0}
.progress-copy{display:flex;justify-content:space-between;font-size:11px;color:var(--muted);margin-bottom:10px}.progress-copy strong{color:var(--text);font:11px var(--mono)}
.progress-track{height:3px;background:var(--line);border-radius:8px;overflow:hidden}.progress-fill{height:100%;width:0;background:var(--accent);transition:width .2s}
.search-box{display:flex;align-items:center;gap:9px;background:var(--bg);border:1px solid var(--line);border-radius:5px;padding:10px 11px;margin-bottom:10px;color:var(--muted)}
.search-box svg{width:15px;height:15px;flex-shrink:0}.search-box:focus-within{border-color:var(--accent)}.search-box input{width:100%;min-width:0;background:none;border:0;outline:0;color:var(--text);font-size:12px;line-height:1.7}.search-box input::placeholder{color:var(--subtle)}
.filter-row{display:grid;grid-template-columns:1fr 1fr;gap:8px;margin-bottom:16px}.filter-row select{width:100%;min-width:0;background:var(--sidebar);color:var(--muted);border:1px solid var(--line);border-radius:5px;padding:8px 5px;font-size:11px}
.drill-list{flex:1;min-height:0;overflow:auto;padding-right:4px;scrollbar-width:thin;scrollbar-color:var(--line) transparent}
.part-label{padding:23px 8px 9px;color:var(--subtle);font-size:9px;line-height:1.75;font-weight:600;letter-spacing:.06em;text-transform:uppercase;word-break:keep-all}.part-label:first-child{padding-top:5px}
.drill-item{width:100%;border:0;border-left:2px solid transparent;background:transparent;color:var(--muted);display:grid;grid-template-columns:31px minmax(0,1fr) 14px;align-items:center;text-align:left;padding:9px 8px;border-radius:0 4px 4px 0;gap:5px;font-size:12px;line-height:1.5;min-height:36px;transition:background .15s,color .15s}
.drill-item:hover{background:var(--panel2);color:var(--text)}.drill-item.active{background:var(--accent-soft);border-left-color:var(--accent);color:var(--text)}.drill-item.active .num{color:var(--accent)}.drill-item.done .state{color:var(--accent)}.drill-item .num{font:10px var(--mono);color:var(--subtle)}.drill-item .title{white-space:nowrap;overflow:hidden;text-overflow:ellipsis}.drill-item .state{text-align:center;color:var(--subtle)}
.side-actions{display:flex;align-items:center;justify-content:space-between;gap:6px;padding-top:16px;margin-top:15px;border-top:1px solid var(--line)}.side-actions .ghost-btn{font-size:10px;padding:7px 8px;background:transparent}.side-actions .text-btn{padding:7px 0}
.main{margin-left:var(--side-width);min-height:100vh}
.topbar{min-height:80px;display:flex;align-items:center;justify-content:space-between;gap:18px;padding:0 46px;border-bottom:1px solid var(--line);position:sticky;top:0;background:var(--topbar);backdrop-filter:blur(12px);z-index:10}
.breadcrumb{display:flex;align-items:center;gap:13px;font-size:11px;color:var(--muted);white-space:nowrap}.breadcrumb .separator{color:var(--subtle)}.breadcrumb a:hover{color:var(--accent)}.crumb{font-size:11px;color:var(--muted)}.top-actions{display:flex;gap:7px;align-items:center}
.hero,.lesson,footer{max-width:var(--max);margin:0 auto;padding-left:clamp(30px,5vw,72px);padding-right:clamp(30px,5vw,72px)}
.hero{padding-top:76px;padding-bottom:64px}
.eyebrow,.section-kicker{font:500 10px/1.7 var(--mono);letter-spacing:.13em;color:var(--accent);text-transform:uppercase}
.hero .eyebrow{display:flex;align-items:center;gap:10px}.hero .eyebrow:before{content:"";width:22px;height:1px;background:var(--accent)}
.hero h1{font-size:clamp(43px,4.8vw,68px);font-weight:580;line-height:1.18;letter-spacing:-.052em;margin:25px 0 25px;max-width:820px;word-break:keep-all}.hero h1 em{font-style:normal;color:var(--accent);font-weight:500}
.hero>p{max-width:550px;color:var(--muted);font-size:15px;line-height:1.95;word-break:keep-all}
.hero-stats{display:grid;grid-template-columns:repeat(4,1fr);border-top:1px solid var(--line);border-bottom:1px solid var(--line);margin:35px 0 27px;padding:22px 0;gap:20px}.hero-stats>div{padding:0 0 0 22px;border-left:1px solid var(--line)}.hero-stats>div:first-child{padding-left:0;border-left:0}.hero-stats strong{display:block;font-size:28px;font-weight:500;letter-spacing:-.05em;line-height:1.3;font-variant-numeric:tabular-nums}.hero-stats span{display:block;color:var(--muted);font:9px var(--mono);margin-top:9px;text-transform:uppercase;letter-spacing:.08em}
.hero-actions{display:flex;gap:10px}.hero-actions .primary-btn:after{content:"↗";margin-left:15px;font-weight:400;font-size:17px}
.note{font-size:10px!important;margin-top:19px!important;line-height:1.9!important}.note code{color:var(--muted);font-size:10px;background:none;padding:0}
.primary-btn,.ghost-btn,.complete-btn,.copy-btn,.icon-btn{display:inline-flex;align-items:center;justify-content:center;border-radius:5px;border:1px solid var(--line);padding:11px 19px;font-size:12px;font-weight:550;line-height:1.5;transition:background .15s,border-color .15s,color .15s}
.primary-btn{background:var(--text);color:var(--bg);border-color:var(--text)}.primary-btn:hover{background:var(--accent);border-color:var(--accent)}
.ghost-btn{background:transparent;color:var(--text)}.ghost-btn:hover{border-color:var(--accent);background:var(--panel2)}.ghost-btn.compact{padding:7px 10px;font-size:11px;border-color:transparent}.ghost-btn.compact:hover{background:var(--panel2)}
.text-btn{background:none;border:0;color:var(--muted);font-size:10px}.text-btn.danger:hover{color:var(--danger)}.icon-btn{padding:7px 10px;background:transparent;color:var(--text);font-size:17px}.mobile-only{display:none}.theme-toggle{min-width:74px}
.practice-loop{display:flex;align-items:center;gap:0;margin-top:43px;padding-top:22px;border-top:1px solid var(--line);max-width:590px;color:var(--muted);font:10px/1.8 var(--mono);letter-spacing:.06em}.practice-loop>span{display:flex;align-items:center;gap:9px;flex:1}.practice-loop b{font-size:9px;color:var(--subtle);font-weight:400}.practice-loop>span:not(:last-child):after{content:"/";margin-left:auto;margin-right:24px;color:var(--line)}
.lesson{padding-top:52px;padding-bottom:60px}.hidden{display:none!important}
.lesson-head{display:flex;justify-content:space-between;align-items:flex-start;gap:24px;margin-bottom:44px;padding-bottom:34px;border-bottom:1px solid var(--line)}.lesson-number{font:10px var(--mono);letter-spacing:.06em;color:var(--subtle);margin-top:24px}.lesson-head h1{font-size:clamp(32px,3.7vw,49px);font-weight:550;line-height:1.24;letter-spacing:-.045em;margin:10px 0 17px;overflow-wrap:anywhere}.lesson-head p{color:var(--muted);max-width:650px;margin:0;font-size:15px;line-height:1.9;word-break:keep-all}.complete-btn{flex-shrink:0;min-width:92px;background:transparent;color:var(--muted);margin-top:5px;padding:9px 13px;font-size:11px}.complete-btn.done{background:var(--accent-soft);border-color:var(--accent-soft);color:var(--accent)}.complete-btn span{margin-right:6px}
.concept-card,.work-card,.challenge-card,.recall-card,.step-card{min-width:0;padding:0;margin-bottom:38px}
.concept-card{padding:0 0 8px}.concept-card h2,.work-card h2,.challenge-card h2,.step-card h2,.recall-card h2{font-size:21px;font-weight:600;margin:11px 0 18px;letter-spacing:-.035em;line-height:1.5}
.concept-card p,.step-card p,.challenge-card p{color:var(--muted);line-height:1.95;word-break:keep-all}.concept-card strong,.concept-card b{color:var(--text);font-weight:600}.concept-card ul,.concept-card ol{padding-left:22px;color:var(--muted)}
.lesson p{overflow-wrap:break-word}.section-title-row{display:flex;align-items:center;justify-content:space-between;gap:10px}.section-title-row h2{margin-bottom:12px}.copy-btn{padding:5px 10px;background:var(--bg);color:var(--muted);font:10px var(--mono);border-radius:4px}.copy-btn:hover{border-color:var(--accent)}.copy-btn.copied{color:var(--accent);border-color:var(--accent)}
pre{margin:12px 0 0;background:var(--code);border:1px solid var(--line);border-radius:6px;padding:24px 26px;overflow:auto;line-height:1.85;tab-size:4;scrollbar-width:thin}code{font-family:var(--mono);font-size:.88em}pre code{color:var(--text);font-size:13px;background:none;padding:0;border-radius:0;white-space:pre}p code,li code{background:var(--panel2);color:var(--text);padding:2px 5px;border-radius:3px;overflow-wrap:anywhere}.command{margin-top:9px;padding:11px 14px;background:var(--sidebar);border:1px solid var(--line);border-radius:4px;font-family:var(--mono);font-size:11px;color:var(--muted);overflow-x:auto;white-space:pre;scrollbar-width:thin}.micro{font-size:11px!important;color:var(--subtle)!important;margin:12px 0 0}
.grid-two{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);gap:36px;padding:28px 0 0;border-top:1px solid var(--line)}.step-card{margin-bottom:24px}.observe-card{border-left:1px solid var(--line);padding-left:34px}.step-card ul,.challenge-card ul{padding-left:20px;color:var(--muted)}.break-card .section-kicker,.observe-card .section-kicker{color:var(--subtle)}
.challenge-card{border-top:1px solid var(--line);padding-top:29px}.challenge-card>div p:first-child{margin-top:0}
details{margin-top:0;border-bottom:1px solid var(--line)}details:first-of-type{border-top:1px solid var(--line);margin-top:25px}summary{padding:17px 0;cursor:pointer;color:var(--text);font-weight:500;font-size:13px;list-style:none;display:flex;align-items:center;justify-content:space-between;gap:20px}summary::-webkit-details-marker{display:none}summary:after{content:"+";font:20px var(--mono);color:var(--muted)}details[open]>summary:after{content:"−"}.details-body{padding:0 0 22px;color:var(--muted);font-size:14px}.details-body pre{margin-top:13px}
.recall-card{display:flex;justify-content:space-between;align-items:center;gap:25px;padding:25px 28px;background:var(--sidebar);border-radius:5px}.recall-card h2{font-size:18px;margin-bottom:10px}.recall-card p{color:var(--muted);margin:0;max-width:540px;font-size:13px;line-height:1.9}.recall-check{white-space:nowrap;display:flex;align-items:center;font-size:11px;color:var(--text)}.recall-check input{accent-color:var(--accent);margin:0 8px 0 0;width:15px;height:15px}
.lesson-nav{display:flex;justify-content:space-between;margin-top:40px;padding-top:24px;border-top:1px solid var(--line)}
footer{padding-top:25px;padding-bottom:20px;color:var(--subtle);font-size:10px;line-height:1.8;border-top:1px solid var(--line)}footer p{margin:0;max-width:700px}.legal{padding-top:0;padding-bottom:32px;border-top:0;font-size:10px;color:var(--subtle)}.legal b{font-weight:500}
.empty{padding:30px 10px;color:var(--muted);font-size:12px}.scrim{display:none}
@media(min-width:1500px){:root{--side-width:306px}.sidebar{padding-left:25px;padding-right:25px}.hero{padding-top:98px}.hero h1{font-size:72px}}
@media(max-width:1100px){:root{--side-width:255px}.sidebar{padding:26px 16px 16px}.topbar{padding:0 30px}.hero,.lesson,footer{padding-left:34px;padding-right:34px}.hero h1{font-size:54px}.hero-stats{gap:12px}.hero-stats>div{padding-left:16px}.grid-two{gap:24px}.observe-card{padding-left:24px}.recall-card{align-items:flex-start;flex-direction:column;gap:18px}}
@media(max-width:900px){
 .sidebar{transform:translateX(-102%);visibility:hidden;transition:transform .2s,visibility .2s;width:min(88vw,320px);padding:26px 22px 20px;box-shadow:none}.sidebar.open{transform:translateX(0);visibility:visible;box-shadow:12px 0 36px var(--shadow)}.main{margin-left:0}.mobile-only{display:inline-flex}.scrim{position:fixed;inset:0;background:rgba(28,39,30,.22);backdrop-filter:blur(2px);z-index:15}.scrim.show{display:block}.topbar{min-height:72px;padding:0 26px;gap:16px}.top-actions{margin-left:auto}.hero,.lesson,footer{padding-left:44px;padding-right:44px}.hero{padding-top:66px}.hero h1{font-size:62px}.drill-item{min-height:39px}.brand small{font-size:10px}.side-actions .ghost-btn{padding:8px 10px;font-size:11px}.filter-row select{font-size:12px}.search-box input{font-size:13px}
}
@media(max-width:560px){
 .topbar{min-height:64px;padding:0 16px;gap:9px}.breadcrumb{font-size:10px;gap:7px}.breadcrumb .crumb,.breadcrumb .separator{display:none}.top-actions{gap:1px}.top-actions .ghost-btn.compact{padding:7px 7px;font-size:10px}.theme-toggle{min-width:66px}.icon-btn{padding:5px 8px}.hero,.lesson,footer{padding-left:24px;padding-right:24px}.hero{padding-top:49px;padding-bottom:40px}.hero .eyebrow{font-size:9px;letter-spacing:.05em;gap:8px}.hero .eyebrow:before{width:15px}.hero h1{font-size:44px;line-height:1.24;margin:23px 0}.hero>p{font-size:14px;line-height:1.9}.hero-stats{margin:30px 0 24px;gap:8px;padding:19px 0}.hero-stats>div{padding-left:11px}.hero-stats strong{font-size:22px}.hero-stats span{font-size:9px;letter-spacing:.01em}.hero-actions{gap:9px}.hero-actions button{font-size:12px;padding:11px 15px}.hero-actions .primary-btn:after{margin-left:12px}.note{font-size:11px!important}.note code{display:block;overflow-wrap:anywhere;font-size:10px;margin-top:3px}.practice-loop{margin-top:29px;padding-top:20px;font-size:9px;letter-spacing:0}.practice-loop>span{gap:5px}.practice-loop>span:not(:last-child):after{margin-right:10px}.practice-loop b{font-size:8px}.lesson{padding-top:32px;padding-bottom:40px}.lesson-head{flex-wrap:wrap;gap:19px;margin-bottom:31px;padding-bottom:26px}.lesson-head>div{flex-basis:100%}.lesson-head h1{font-size:35px;line-height:1.25}.lesson-head p{font-size:14px}.lesson-number{margin-top:17px}.complete-btn{margin:0;padding:8px 12px}.concept-card,.work-card,.challenge-card{margin-bottom:30px}.concept-card h2,.work-card h2,.step-card h2,.challenge-card h2{font-size:20px}.concept-card p,.step-card p,.challenge-card p{font-size:14px}.section-kicker{font-size:9px}.grid-two{grid-template-columns:1fr;gap:0;padding-top:23px}.observe-card{padding:24px 0 0;border-left:0;border-top:1px solid var(--line)}.step-card{margin-bottom:25px}.challenge-card{padding-top:25px}pre{padding:20px 18px;line-height:1.8}pre code{font-size:12px}.command{font-size:10px;padding:11px 12px}.recall-card{padding:21px}.recall-check{padding:4px 0}.lesson-nav{gap:10px}.lesson-nav button{flex:1;padding:10px 8px;font-size:11px}footer,.legal{font-size:10px}
}
@media(max-width:359px){.hero h1{font-size:38px}.hero,.lesson,footer{padding-left:20px;padding-right:20px}.hero-stats strong{font-size:19px}.topbar{gap:4px;padding:0 11px}.top-actions .ghost-btn.compact{padding:7px 5px}.breadcrumb{font-size:9px}.practice-loop>span:not(:last-child):after{margin-right:6px}.hero-actions .primary-btn:after{margin-left:6px}.hero-actions button{padding:10px 12px}}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,*:before,*:after{transition:none!important}}
@media print{.sidebar,.topbar,.lesson-nav,.copy-btn,.complete-btn,.hero-actions,.scrim,.skip-link{display:none!important}.main{margin:0}.lesson,.hero,footer{max-width:none;padding-left:0;padding-right:0}body{background:#fff;color:#111}.hidden{display:none!important}pre{white-space:pre-wrap;border:1px solid #ddd}pre code{white-space:pre-wrap}.grid-two{display:block}.observe-card{border-left:0;padding-left:0}.lesson-head{break-after:avoid}}