:root {
    --bg:#fff;
    --fg:#0a0a0a;
    --text:#171717;
    --muted:#525252;
    --faint:#a3a3a3;
    --line:#ebebeb;
    --hover:rgba(0,0,0,0.045);
    --line-soft:rgba(0,0,0,0.07);
    --accent:#f76b15;
    --accent-hover:#e05a0a;
    --top-h:60px;
    --display:"Manrope";
    --body:"Inter";
}

* {
    box-sizing:border-box;
    margin:0;
    padding:0;
}

[hidden] {
    display:none !important;
}

body {
    background:var(--bg);
    color:var(--text);
    font-family:var(--body);
    -webkit-font-smoothing:antialiased;
    background:linear-gradient(to bottom,rgba(247,107,21,0.16),rgba(253,186,116,0.08) 280px,rgba(255,255,255,0) 560px) no-repeat, var(--bg);
}


a {
    color:inherit;
    text-decoration:none;
}

button {
    font:inherit;
    color:inherit;
}

.topbar {
    position:sticky;
    top:0;
    z-index:30;
    height:var(--top-h);
    display:flex;
    align-items:center;
    gap:32px;
    padding:0 24px;;
    background:rgba(255,255,255,0.35);
    -webkit-backdrop-filter:blur(14px);
    backdrop-filter:blur(14px);
    border-bottom:2px solid var(--line-soft);
}

.logo {
    font-family:var(--display);
    font-size:21px;
    font-weight:700;
    letter-spacing:-0.035em;
    line-height:1;
    color:var(--fg);
}

.nav {
    display:flex;
    gap:4px;
    list-style:none;
}

.tbtn {
    display:flex;
    align-items:center;
    gap:6px;
    height:34px;
    padding:0 12px;
    border:none;
    border-radius:10px;
    background:none;
    color:var(--muted);
    font-size:14px;
    font-weight:500;
    white-space:nowrap;
    cursor:pointer;
    transition:background 0.15s,color 0.15s;
}

.tbtn:hover,
.btn[aria-expanded="true"] {
    background:var(--hover);
    color:var(--fg);
} 

.tbtn svg {
    width:15px;
    height:15px;
    color:var(--faint);
}

.tbtn--strong {
    color:var(--fg);
}

.tbtn--solid {
    margin-left:4px;
    background:var(--accent);
    color:#fff;
}

.tbtn--solid:hover {
    background:var(--accent-hover);
    color:#fff;
}

.actions {
    display:flex;
    align-items:center;
    gap:4px;
    margin-left:auto;
}

.picker {
    display:flex;
    align-items:center;
    height:34px;
    margin-right:8px;
    border:2px solid var(--line-soft);
    border-radius:11px;
}

.picker .tbtn {
    height:30px;
    border-radius:9px;
}

.picker__divider {
    width:2px;
    height:18px;
    background:var(--line-soft);
}

.picker .placeholder {
    color:var(--faint);
}

.drop {
    position:relative;
}

.menu {
    position:absolute;
    top:calc(100% + 8px);
    left:0;
    min-width:180px;
    padding:6px;
    background:var(--bg);
    border:2px solid var(--line);
    border-radius:12px;
}

.menu__item {
    display:flex;
    align-items:center;
    width:100%;
    padding:8px 10px;
    border:none;
    border-radius:8px;
    background:none;
    font-size:14px;
    font-weight:500;
    text-align:left;
    cursor:pointer;
    transition:background 0.15s;
}

.menu__item:hover {
    background:var(--hover);
}

.menu__item .tick {
    width:16px;
    height:16px;
    margin-left:auto;
    visibility:hidden;
}

.menu__item.selected .tick {
    visibility:visible;
}

main {
    position:relative;
    display:flex;
    flex-direction:column;
    min-height:calc(100vh - var(--top-h));
    overflow:hidden;
}

.doodles {
    position:absolute;
    inset:0;
    z-index:-1;
    pointer-events:none;
}

.doodles span {
    position:absolute;
    left:var(--x);
    top:var(--y);
    width:var(--s);
    height:var(--s);
    color:rgba(247,101,27,0.2);
    transform:translate(-50%,-50%) rotate(var(--r));
}

.doodles svg {
    display:block;
    width:100%;
    height:100%;
}

.hero {
    position:relative;
    z-index:0;
    max-width:1080px;
    margin:0 auto;
    flex:1;
    width:100%;
    padding:clamp(40px,11vh,112px) 40px clamp(32px,7vh,72px);
    display:grid;
    grid-template-columns:minmax(0,520px) minmax(0,400px);
    justify-content:space-between;
    align-items:center;
    column-gap:64px;
}

.hero__title {
    color:var(--fg);
    font-family:var(--display);
    font-size:clamp(36px,4.6vw,54px);
    font-weight:700;
    letter-spacing:-0.045em;
    line-height:1.05;
}

.hero__title span {
    font-weight:800;
}

.hero__sub {
    max-width:420px;
    margin-top:20px;
    color:var(--muted);
    font-size:17px;
    line-height:1.55;
    letter-spacing:-0.01em;
}

.hero__cta {
    margin-top:32px;
}

.demo {
    padding:22px 22px 18px;
    background:var(--bg);
    border:2px solid var(--line);
    border-radius:18px;
    -webkit-user-select:none;
    user-select:none;
    cursor:default;
}

.demo__top {
    display:flex;
    align-items:center;
    justify-content:space-between;
    margin-bottom:14px;
}

.demo__heading {
    display:flex;
    align-items:center;
    gap:8px;
    min-width:0;
}

.demo__grade {
    flex-shrink:0;
    padding:3px 8px;
    border-radius:7px;
    background:rgba(247,107,21,0.1);
    color:#c2410c;
    font-size:12px;
    font-weight:600;
}

.demo__topic {
    overflow:hidden;
    color:var(--faint);
    font-size:13px;
    font-weight:500;
    white-space:nowrap;
    text-overflow:ellipsis;
}

.demo__title {
    flex-shrink:0;
    color:var(--fg);
    font-family:var(--display);
    font-size:18px;
    font-weight:700;
    letter-spacing:-0.02em;
}

.calc {
    position:relative;
    display:grid;
    place-items:center;
    width:30px;
    height:30px;
    color:var(--muted);
}

.calc > svg {
    width:22px;
    height:22px;
}

.calc__badge {
    position:absolute;
    right:-2px;
    bottom:0;
    display:none;
    place-items:center;
    width:15px;
    height:15px;
    border:2px solid var(--bg);
    border-radius:50%;
    color:#fff;
}

.calc__badge--yes {
    background:#22c55e;
}

.calc__badge--no {
    display:grid;
    background:#ef4444;
}

.calc__badge svg {
    width:9px;
    height:9px;
    stroke-width:3.5;
}

.calc.is-allowed .calc__badge--yes {
    display:grid;
}

.calc.is-allowed .calc__badge--no {
    display:none;
}

.demo__text {
    color:var(--fg);
    font-size:16px;
    line-height:1.6;
}

.demo .katex {
    font-size:1.15em;
}

.demo__answer {
    display:flex;
    flex-direction:column;
    gap:10px;
    margin-top:18px;
}

.demo__box {
    display:flex;
    align-items:center;
    height:44px;
    padding:0 14px;
    border:2px solid var(--line);
    border-radius:10px;
    color:var(--fg);
    font-size:16px;
    transition:border-color 0.2s, background 0.2s;
}

.demo__box::after {
    content:"";
    width:1.5px;
    height:20px;
    margin-left:2px;
    background:var(--fg);
    animation:blink 1s steps(1) infinite;
}

.demo.is-marked .demo__box {
    border-color:#22c55e;
    background:#f0fdf4;
}

.demo.is-marked .demo__box::after {
    display:none;
}

@keyframes blink {
    50% {
        opacity:0;
    }
}

.demo__check {
    height:44px;
    padding:0 16px;
    border:none;
    border-radius:10px;
    background:var(--accent);
    color:#fff;
    font-size:14px;
    font-weight:500;
    transition:transform 0.1s,background 0.15s;
}

.demo__check.is-pressed {
    transform:scale(0.95);
    background:var(--accent-hover);
}

.demo__foot {
    display:flex;
    align-items:center;
    justify-content:space-between;
    min-height:28px;
    margin-top:14px;
}

.demo__mark {
    display:flex;
    align-items:center;
    gap:6px;
    color:#16a34a;
    font-size:14px;
    font-weight:500;
    opacity:0;
    transform:translateY(4px);
    transition:opacity 0.25s,transform 0.25s;
}

.demo__mark svg {
    width:16px;
    height:16px;
}

.demo.is-marked .demo__mark {
    opacity:1;
    transform:none;
}

.demo__marks {
    color:var(--faint);
    font-size:13px;
}

.demo__body {
    transition:opacity 0.3s;
}

.demo__body.is-hidden {
    opacity:0;
}

.btn {
    display:inline-flex;
    align-items:center;
    gap:8px;
    height:50px;
    padding:0 20px 0 24px;
    border-radius:16px;
    background:var(--accent);
    color:#fff;
    font-size:16px;
    font-weight:500;
    white-space:nowrap;
    transition:background 0.15s;
}

.btn:hover {
    background:var(--accent-hover);
}

.btn svg {
    width:18px;
    height:18px;
    transform:transform 0.2s;
}

.btn:hover svg {
    transition:translateX(3px);
}

.topics {
    flex-shrink:0;
    padding:8px 0 clamp(40px,8vh,80px);
    overflow:hidden;
    -webkit-mask-image:linear-gradient(to right, transparent, #000 10%,#000 90%,transparent);
    mask-image:linear-gradient(to right,transparent,#000 10%,#000 90%,transparent);
}

.topics__track {
    display:flex;
    gap:14px;
    width:max-content;
    animation:slide-left 40s linear infinite;
}

.topics:hover .topics__track {
    animation-play-state:paused;
}

@keyframes slide-left {
    to {
        transform:translateX(calc(-50% - 7px));
    }
}

.feature {
    position:relative;
    display:flex;
    align-items:center;
    gap:14px;
    width:330px;
    height:104px;
    padding:0 20px 0 18px;
    overflow:hidden;
    border-radius:20px;
    background:var(--c);
    color:var(--ink);
    -webkit-user-select:none;
    user-select:none;
}

.feature__badge {
    flex-shrink:0;
    display:grid;
    place-items:center;
    width:44px;
    height:44px;
    border-radius:13px;
    background:color-mix(in srgb,var(--ink) 14%,transparent);
}

.feature__badge svg {
    width:21px;
    height:21px;
}

.feature__body {
    position:relative;
    min-width:0;
}

.feature__name {
    display:flex;
    align-items:center;
    gap:8px;
    font-family:var(--display);
    font-size:17px;
    font-weight:700;
    letter-spacing:-0.02em;
}

.feature__text {
    margin-top:3px;
    font-size:13.5px;
    line-height:1.4;
    opacity:0.8;
}

.feature__icon {
    position:absolute;
    right:-18px;
    bottom:-22px;
    width:96px;
    height:96px;
    opacity:0.1;
    transform:rotate(-14deg);
    pointer-events:none;
}