/* ==========================================================================
   Listing pages — HLD / LLD / DSA index grids.
   Shared hero, progress strip, filter bar, difficulty groups, problem cards,
   study roadmap, and the completion celebration modal. Chrome comes from
   core.css; this is the catalogue composition. All colours are tokens.
   ========================================================================== */

/* --------------------------------------------------------------------------
   Hero
   -------------------------------------------------------------------------- */
.hero {
    position: relative;
    z-index: 1;
    max-width: var(--measure);
    margin: 0 auto;
    padding: var(--sp-8) var(--sp-5) var(--sp-5);
    text-align: center;
}
.hero-badge {
    display: inline-block;
    background: var(--accent-subtle);
    border: 1px solid var(--border-accent);
    color: var(--accent);
    padding: 0.35rem 0.9rem;
    border-radius: var(--r-full);
    font-size: var(--fs-xs);
    font-weight: 700;
    letter-spacing: 0.02em;
    margin-bottom: var(--sp-4);
}
.hero h1 {
    font-size: var(--fs-3xl);
    font-weight: 800;
    letter-spacing: -0.035em;
    line-height: 1.1;
    color: var(--text);
    margin-bottom: var(--sp-4);
    text-wrap: balance;
}
.hero h1 em {
    font-style: normal;
    background: linear-gradient(135deg, var(--accent), var(--accent-hover));
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}
.hero p {
    color: var(--text-muted);
    font-size: var(--fs-lg);
    line-height: 1.65;
    max-width: 64ch;
    margin: 0 auto var(--sp-5);
    text-wrap: pretty;
}
.hero-stats { display: flex; justify-content: center; gap: var(--sp-7); margin-top: var(--sp-5); flex-wrap: wrap; }
.hero-stat { text-align: center; }
.hero-stat strong { display: block; font-size: var(--fs-2xl); color: var(--text); font-weight: 800; letter-spacing: -0.02em; }
.hero-stat span { font-size: var(--fs-sm); color: var(--text-dim); }

/* --------------------------------------------------------------------------
   Progress strip
   -------------------------------------------------------------------------- */
.progress-strip { position: relative; z-index: 1; max-width: var(--measure); margin: 0 auto var(--sp-6); padding: 0 var(--sp-5); }
.progress-inner {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--r-md);
    padding: var(--sp-3) var(--sp-4);
    display: flex;
    align-items: center;
    gap: var(--sp-4);
}
.progress-label { font-size: var(--fs-sm); color: var(--text-muted); white-space: nowrap; font-weight: 500; }
.progress-bar-track { flex: 1; height: 6px; background: var(--surface-3); border-radius: var(--r-full); overflow: hidden; }
.progress-bar-fill { height: 100%; background: linear-gradient(90deg, var(--accent), #a78bfa); border-radius: var(--r-full); transition: width 0.4s var(--ease); width: 0%; }

/* --------------------------------------------------------------------------
   Sections
   -------------------------------------------------------------------------- */
.section { position: relative; z-index: 1; max-width: var(--measure); margin: 0 auto; padding: 0 var(--sp-5) var(--sp-6); }

/* --------------------------------------------------------------------------
   "Start here" callouts
   -------------------------------------------------------------------------- */
.start-here {
    display: flex;
    align-items: center;
    gap: var(--sp-4);
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--r-md);
    padding: var(--sp-4) var(--sp-5);
    text-decoration: none;
    color: var(--text);
    transition: border-color var(--dur) var(--ease), transform var(--dur) var(--ease);
}
.start-here:hover { border-color: var(--border-accent); transform: translateY(-2px); }
.start-here-content strong { font-size: var(--fs-base); color: var(--text); }
.start-here-content p { font-size: var(--fs-sm); color: var(--text-muted); margin-top: 0.2rem; }
.start-here-arrow { font-size: 1.2rem; color: var(--accent); margin-left: auto; }

/* --------------------------------------------------------------------------
   Filter bar
   -------------------------------------------------------------------------- */
.filter-bar { display: flex; gap: var(--sp-2); flex-wrap: wrap; margin-bottom: var(--sp-2); }
.filter-btn {
    background: var(--surface);
    border: 1px solid var(--border);
    color: var(--text-muted);
    padding: 0.5rem 1rem;
    min-height: 40px;
    border-radius: var(--r-sm);
    font-size: var(--fs-sm);
    font-weight: 500;
    cursor: pointer;
    transition: border-color var(--dur-fast) var(--ease), color var(--dur-fast) var(--ease),
                background var(--dur-fast) var(--ease);
}
.filter-btn:hover { border-color: var(--border-accent); color: var(--text); }
.filter-btn.active { background: var(--accent); color: var(--accent-contrast); border-color: var(--accent); }

.section-header { display: flex; align-items: center; justify-content: space-between; margin-bottom: var(--sp-4); gap: var(--sp-3); }
.section-header h2 { font-size: var(--fs-lg); font-weight: 700; color: var(--text); letter-spacing: -0.02em; }
.section-count { font-size: var(--fs-xs); color: var(--text-dim); white-space: nowrap; }

/* --------------------------------------------------------------------------
   Difficulty groups
   -------------------------------------------------------------------------- */
.difficulty-group { margin-bottom: var(--sp-7); }
.group-header { display: flex; align-items: center; justify-content: space-between; margin-bottom: var(--sp-4); }
.group-header h2 { font-size: var(--fs-lg); font-weight: 700; color: var(--text); display: flex; align-items: center; gap: var(--sp-2); }
.group-count { font-size: var(--fs-xs); color: var(--text-dim); }
.diff-dot { width: 10px; height: 10px; border-radius: 50%; display: inline-block; }
.diff-dot.green { background: var(--easy); }
.diff-dot.yellow { background: var(--medium); }
.diff-dot.red { background: var(--hard); }

/* --------------------------------------------------------------------------
   Problem cards
   -------------------------------------------------------------------------- */
.problems-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: var(--sp-4); }
/* Frosted glass over the page mesh — see .surface-card in core.css. */
.problem-card {
    position: relative;
    background: var(--card-glass);
    backdrop-filter: blur(var(--card-blur));
    -webkit-backdrop-filter: blur(var(--card-blur));
    border: 1px solid var(--border);
    border-radius: var(--r-lg);
    padding: var(--sp-4);
    text-decoration: none;
    color: var(--text);
    display: flex;
    flex-direction: column;
    box-shadow: var(--shadow-md);
    transition: background var(--dur) var(--ease), border-color var(--dur) var(--ease),
                transform var(--dur) var(--ease), box-shadow var(--dur) var(--ease);
}
.problem-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: var(--r-lg);
    right: var(--r-lg);
    height: 1px;
    background: var(--card-sheen);
    opacity: 0.7;
    pointer-events: none;
}
.problem-card:hover {
    background: var(--card-glass-hover);
    border-color: var(--border-accent);
    transform: translateY(-3px);
    box-shadow: var(--shadow-lg), var(--glow-accent);
}
.card-top { display: flex; justify-content: space-between; align-items: center; margin-bottom: var(--sp-3); gap: var(--sp-2); }
.card-icon { font-size: 1.5rem; }
.status-badge, .diff-badge { font-size: var(--fs-xs); font-weight: 600; padding: 3px 9px; border-radius: var(--r-xs); }
.status-badge.live { background: color-mix(in srgb, var(--success) 12%, transparent); color: var(--success); border: 1px solid color-mix(in srgb, var(--success) 25%, transparent); }
.status-badge.soon { background: color-mix(in srgb, var(--warning) 12%, transparent); color: var(--warning); border: 1px solid color-mix(in srgb, var(--warning) 25%, transparent); }
.diff-badge.green { background: color-mix(in srgb, var(--easy) 12%, transparent); color: var(--easy); border: 1px solid color-mix(in srgb, var(--easy) 25%, transparent); }
.diff-badge.yellow { background: color-mix(in srgb, var(--medium) 12%, transparent); color: var(--medium); border: 1px solid color-mix(in srgb, var(--medium) 25%, transparent); }
.diff-badge.red { background: color-mix(in srgb, var(--hard) 12%, transparent); color: var(--hard); border: 1px solid color-mix(in srgb, var(--hard) 25%, transparent); }
.problem-card.coming-soon { opacity: 0.6; cursor: default; }
.problem-card h3 { font-size: var(--fs-md); font-weight: 700; margin-bottom: 0.4rem; color: var(--text); }
.card-desc { font-size: var(--fs-sm); color: var(--text-muted); margin-bottom: var(--sp-3); flex-grow: 1; line-height: 1.55; }
.card-time { display: block; margin-top: var(--sp-2); font-size: var(--fs-xs); color: var(--text-dim); }
.card-tags { display: flex; gap: var(--sp-2); flex-wrap: wrap; margin-bottom: var(--sp-2); }
.tag { background: var(--accent-subtle); border: 1px solid var(--border-accent); color: var(--accent); padding: 2px 9px; border-radius: var(--r-xs); font-size: var(--fs-xs); font-weight: 500; }
.card-companies { display: flex; gap: var(--sp-2); flex-wrap: wrap; }
.company { font-size: var(--fs-xs); color: var(--text-dim); background: var(--surface-2); border: 1px solid var(--border); padding: 2px 8px; border-radius: var(--r-xs); }

/* Footer row on LLD cards: companies on the left, languages on the right */
.card-meta { display: flex; justify-content: space-between; align-items: center; gap: var(--sp-3); flex-wrap: wrap; }
.card-lang { display: flex; gap: var(--sp-1); flex-wrap: wrap; }
.lang { font-size: var(--fs-xs); color: var(--accent); background: var(--accent-subtle); border: 1px solid var(--border-accent); padding: 2px 7px; border-radius: var(--r-xs); font-weight: 500; }

.card-check { width: 16px; height: 16px; accent-color: var(--accent); cursor: pointer; margin-left: 0.5rem; flex-shrink: 0; }

/* --------------------------------------------------------------------------
   "Simulate" chip (injected by JS on HLD cards)
   -------------------------------------------------------------------------- */
.sim-chip {
    display: inline-flex;
    align-items: center;
    gap: 5px;
    font-size: var(--fs-xs);
    font-weight: 600;
    padding: 3px 10px;
    border-radius: var(--r-full);
    cursor: pointer;
    background: var(--accent-subtle);
    color: var(--accent);
    border: 1px solid var(--border-accent);
    text-decoration: none;
    transition: background var(--dur-fast) var(--ease), color var(--dur-fast) var(--ease),
                transform var(--dur-fast) var(--ease);
    white-space: nowrap;
}
.sim-chip::before { content: "▸"; font-size: 0.7rem; }
.sim-chip:hover { background: var(--accent); color: var(--accent-contrast); transform: translateY(-1px); }

/* --------------------------------------------------------------------------
   Study roadmap
   -------------------------------------------------------------------------- */
.roadmap-card { background: var(--surface); border: 1px solid var(--border); border-radius: var(--r-lg); padding: var(--sp-6); }
.roadmap-card h2 { font-size: var(--fs-lg); font-weight: 700; margin-bottom: 0.3rem; color: var(--text); }
.roadmap-sub { font-size: var(--fs-sm); color: var(--text-muted); margin-bottom: var(--sp-5); }
.roadmap-steps { display: flex; flex-direction: column; gap: var(--sp-3); }
.step {
    display: flex;
    align-items: center;
    gap: var(--sp-4);
    padding: var(--sp-3) var(--sp-4);
    background: var(--surface-2);
    border: 1px solid var(--border);
    border-radius: var(--r-md);
    transition: border-color var(--dur) var(--ease);
}
.step:hover { border-color: var(--border-accent); }
.step-num { width: 28px; height: 28px; background: var(--accent); color: var(--accent-contrast); border-radius: 50%; display: flex; align-items: center; justify-content: center; font-size: var(--fs-xs); font-weight: 700; flex-shrink: 0; }
.step-content strong { display: block; font-size: var(--fs-sm); color: var(--text); }
.step-content span { font-size: var(--fs-sm); color: var(--text-muted); }
.step-link { margin-left: auto; font-size: var(--fs-sm); color: var(--accent); text-decoration: none; font-weight: 500; white-space: nowrap; }

/* --------------------------------------------------------------------------
   Grading rubric card (LLD)
   -------------------------------------------------------------------------- */
.grading-card { background: var(--surface); border: 1px solid var(--border); border-radius: var(--r-lg); padding: var(--sp-6); }
.grading-card h2 { font-size: var(--fs-lg); font-weight: 700; margin-bottom: var(--sp-5); color: var(--text); letter-spacing: -0.02em; }
.grading-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); gap: var(--sp-3); }
.grade-item {
    display: flex;
    align-items: flex-start;
    gap: var(--sp-3);
    padding: var(--sp-3) var(--sp-4);
    background: var(--surface-2);
    border: 1px solid var(--border);
    border-radius: var(--r-md);
    transition: border-color var(--dur) var(--ease);
}
.grade-item:hover { border-color: var(--border-accent); }
.grade-num {
    width: 24px; height: 24px;
    background: var(--accent); color: var(--accent-contrast);
    border-radius: 50%;
    display: flex; align-items: center; justify-content: center;
    font-size: var(--fs-xs); font-weight: 700;
    flex-shrink: 0; margin-top: 2px;
}
.grade-content strong { display: block; font-size: var(--fs-sm); color: var(--text); margin-bottom: 0.15rem; }
.grade-content span { font-size: var(--fs-sm); color: var(--text-muted); line-height: 1.5; }

/* --------------------------------------------------------------------------
   Entrance animation
   -------------------------------------------------------------------------- */
.reveal { opacity: 0; transform: translateY(18px); transition: opacity 0.5s var(--ease), transform 0.5s var(--ease); }
.reveal.visible { opacity: 1; transform: translateY(0); }

/* --------------------------------------------------------------------------
   Completion celebration modal
   -------------------------------------------------------------------------- */
#celebration-overlay { position: fixed; inset: 0; z-index: 9999; display: flex; align-items: center; justify-content: center; }
#celebration-overlay.celeb-closing { animation: celeb-fadeout 0.4s ease forwards; }
@keyframes celeb-fadeout { to { opacity: 0; } }

.celeb-backdrop { position: absolute; inset: 0; background: rgba(0,0,0,0.5); backdrop-filter: blur(6px); animation: celeb-fadein 0.3s ease; }
[data-theme="light"] .celeb-backdrop { background: rgba(255,255,255,0.6); }
@keyframes celeb-fadein { from { opacity: 0; } to { opacity: 1; } }

.celeb-confetti-container { position: absolute; inset: 0; pointer-events: none; overflow: hidden; }
.celeb-piece { position: absolute; opacity: 0; animation: celeb-burst ease-out forwards; }
@keyframes celeb-burst {
    0% { opacity: 1; transform: translate(0, 0) rotate(0deg) scale(1); }
    70% { opacity: 1; }
    100% { opacity: 0; transform: translate(var(--x-end), var(--y-end)) rotate(var(--r-end)) scale(0.3); }
}

.celeb-modal {
    position: relative;
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: var(--r-xl);
    padding: var(--sp-6) var(--sp-7);
    text-align: center;
    max-width: 340px;
    width: 90vw;
    box-shadow: var(--shadow-lg);
    animation: celeb-modal-in 0.5s cubic-bezier(0.34, 1.56, 0.64, 1) 0.15s both;
}
@keyframes celeb-modal-in { from { opacity: 0; transform: scale(0.8) translateY(20px); } to { opacity: 1; transform: scale(1) translateY(0); } }

.celeb-badge {
    width: 64px;
    height: 64px;
    margin: 0 auto var(--sp-4);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--accent-subtle);
    border: 2px solid var(--border-accent);
    animation: celeb-badge-pop 0.5s cubic-bezier(0.34, 1.56, 0.64, 1) 0.4s both;
}
@keyframes celeb-badge-pop { from { transform: scale(0); } to { transform: scale(1); } }

.celeb-modal h2 { color: var(--text); font-size: var(--fs-lg); font-weight: 700; margin-bottom: 0.4rem; animation: celeb-text-in 0.4s ease 0.5s both; }
.celeb-modal p { color: var(--text-muted); font-size: var(--fs-sm); line-height: 1.5; margin-bottom: var(--sp-5); animation: celeb-text-in 0.4s ease 0.6s both; }
@keyframes celeb-text-in { from { opacity: 0; transform: translateY(8px); } to { opacity: 1; transform: translateY(0); } }

.celeb-btn {
    background: var(--accent);
    color: var(--accent-contrast);
    border: none;
    padding: 0.65rem 2rem;
    min-height: 44px;
    border-radius: var(--r-md);
    font-size: var(--fs-sm);
    font-weight: 600;
    cursor: pointer;
    transition: transform var(--dur-fast) var(--ease), box-shadow var(--dur-fast) var(--ease);
    box-shadow: var(--shadow-accent);
    animation: celeb-text-in 0.4s ease 0.7s both;
}
.celeb-btn:hover { transform: translateY(-1px); }
.celeb-btn:active { transform: translateY(0); }

/* --------------------------------------------------------------------------
   Responsive
   -------------------------------------------------------------------------- */
@media (max-width: 860px) {
    .sim-chip { display: none; }
}
@media (max-width: 640px) {
    .hero { padding: var(--sp-6) var(--sp-5) var(--sp-4); }
    .hero-stats { gap: var(--sp-5); }
    .problems-grid { grid-template-columns: 1fr; }
    .grading-grid { grid-template-columns: 1fr; }
    .grading-card { padding: var(--sp-5) var(--sp-4); }
    .start-here { flex-direction: column; text-align: center; }
    .start-here-arrow { margin-left: 0; }
    .step { flex-wrap: wrap; }
    .step-link { margin-left: 0; }
}