:root {
	--bg: #f7efe4;
	--bg-strong: #eadcc7;
	--panel: rgba(255, 252, 247, 0.84);
	--panel-strong: #fffaf3;
	--border: rgba(68, 47, 24, 0.16);
	--text: #23170d;
	--muted: #6f5c46;
	--accent: #ad4325;
	--accent-soft: #ffe0cd;
	--accent-strong: #7b2a12;
	--success: #0f6f52;
	--warning: #8c5a13;
	--shadow: 0 18px 48px rgba(68, 47, 24, 0.12);
	--radius: 22px;
	--mono: "IBM Plex Mono", "SFMono-Regular", Consolas, monospace;
	--serif: "Iowan Old Style", "Palatino Linotype", "Book Antiqua", Georgia,
		serif;
	--sans: "Avenir Next", "Segoe UI", system-ui, sans-serif;
}

* {
	box-sizing: border-box;
}

html {
	scroll-behavior: smooth;
}

body {
	margin: 0;
	font-family: var(--sans);
	color: var(--text);
	background:
		radial-gradient(circle at top left, rgba(255, 212, 177, 0.9), transparent 28%),
		radial-gradient(circle at top right, rgba(250, 237, 195, 0.85), transparent 24%),
		linear-gradient(180deg, #fcf5ea 0%, var(--bg) 48%, #efe4d4 100%);
	min-height: 100vh;
}

a {
	color: var(--accent-strong);
}

.page-shell {
	display: grid;
	grid-template-columns: minmax(280px, 330px) minmax(0, 1fr);
	gap: 28px;
	max-width: 1500px;
	margin: 0 auto;
	padding: 26px;
}

.sidebar {
	position: sticky;
	top: 0;
	align-self: start;
	padding: 28px;
	border-radius: calc(var(--radius) + 8px);
	background:
		linear-gradient(180deg, rgba(255, 252, 247, 0.92), rgba(248, 239, 225, 0.82)),
		var(--panel);
	border: 1px solid var(--border);
	box-shadow: var(--shadow);
	backdrop-filter: blur(16px);
	max-height: calc(100vh - 52px);
	overflow: auto;
}

.sidebar h1,
.content h2,
.content h3,
.content h4 {
	font-family: var(--serif);
	letter-spacing: -0.02em;
	margin: 0 0 12px;
}

.sidebar h1 {
	font-size: clamp(2.2rem, 4vw, 3.2rem);
	line-height: 0.94;
}

.sidebar-copy,
.card p,
.explanation-box,
.quiz-result,
.lab-output,
.callout p,
.clean-list li {
	line-height: 1.65;
	font-size: 1rem;
}

.eyebrow {
	margin: 0 0 10px;
	text-transform: uppercase;
	letter-spacing: 0.18em;
	font-size: 0.78rem;
	color: var(--muted);
}

.panel,
.lesson,
.card,
.callout {
	border: 1px solid var(--border);
	box-shadow: var(--shadow);
}

.panel {
	background: rgba(255, 252, 247, 0.86);
	border-radius: 20px;
	padding: 18px;
	margin-top: 22px;
}

.panel-head,
.card-head,
.lesson-top {
	display: flex;
	align-items: center;
	justify-content: space-between;
	gap: 12px;
}

.nav-panel {
	display: grid;
	gap: 10px;
}

.nav-panel a {
	padding: 10px 12px;
	border-radius: 12px;
	background: rgba(255, 247, 238, 0.8);
	text-decoration: none;
	font-weight: 600;
	transition:
		transform 0.16s ease,
		background 0.16s ease;
}

.nav-panel a:hover,
.nav-panel a:focus-visible {
	background: var(--accent-soft);
	transform: translateX(4px);
}

.progress-track {
	height: 13px;
	background: rgba(137, 112, 82, 0.14);
	border-radius: 999px;
	overflow: hidden;
	margin: 12px 0 14px;
}

.progress-fill {
	height: 100%;
	width: 0;
	background: linear-gradient(90deg, var(--accent), #d57339);
	border-radius: inherit;
	transition: width 0.25s ease;
}

.ghost-button,
button {
	border: 1px solid rgba(123, 42, 18, 0.2);
	border-radius: 999px;
	background: rgba(255, 252, 247, 0.9);
	color: var(--text);
	font: inherit;
	padding: 10px 14px;
	cursor: pointer;
	transition:
		transform 0.16s ease,
		background 0.16s ease,
		border-color 0.16s ease;
}

button:hover,
button:focus-visible,
.ghost-button:hover,
.ghost-button:focus-visible {
	transform: translateY(-1px);
	border-color: rgba(123, 42, 18, 0.42);
	background: rgba(255, 242, 232, 1);
}

.content {
	display: grid;
	gap: 24px;
}

.lesson,
.extra-lesson {
	padding: 26px;
	background:
		linear-gradient(180deg, rgba(255, 252, 247, 0.95), rgba(250, 242, 232, 0.9)),
		var(--panel-strong);
	border-radius: calc(var(--radius) + 2px);
}

.lesson.is-complete {
	border-color: rgba(15, 111, 82, 0.3);
	box-shadow:
		var(--shadow),
		inset 0 0 0 2px rgba(15, 111, 82, 0.08);
}

.lesson-check {
	display: inline-flex;
	align-items: center;
	gap: 10px;
	font-weight: 600;
}

.lesson-check input {
	inline-size: 18px;
	block-size: 18px;
	accent-color: var(--success);
}

.two-column,
.three-column,
.interactive-grid,
.flashcard-grid {
	display: grid;
	gap: 18px;
}

.two-column {
	grid-template-columns: repeat(2, minmax(0, 1fr));
}

.three-column {
	grid-template-columns: repeat(3, minmax(0, 1fr));
}

.interactive-grid {
	grid-template-columns: minmax(0, 1.05fr) minmax(0, 0.95fr);
	align-items: start;
}

.card {
	padding: 20px;
	border-radius: 18px;
	background: rgba(255, 252, 247, 0.88);
}

.interactive-card {
	background:
		linear-gradient(180deg, rgba(255, 245, 235, 0.96), rgba(255, 251, 246, 0.88)),
		white;
}

.callout {
	margin-top: 18px;
	padding: 18px 20px;
	border-radius: 18px;
	background: rgba(255, 240, 228, 0.9);
}

.callout.warning {
	background: rgba(255, 244, 224, 0.95);
	border-color: rgba(140, 90, 19, 0.24);
}

.quote {
	font-family: var(--serif);
	font-size: 1.2rem;
}

.code-block,
.diagram {
	padding: 16px 18px;
	border-radius: 16px;
	font-family: var(--mono);
	font-size: 0.94rem;
	line-height: 1.6;
	white-space: pre-wrap;
	overflow-x: auto;
	border: 1px solid rgba(68, 47, 24, 0.12);
}

.code-block {
	background: #20140e;
	color: #fff5ea;
}

.diagram {
	background: #f2e7d9;
	color: #2b1d11;
}

.clean-list {
	margin: 0;
	padding-left: 20px;
}

.button-row {
	display: flex;
	flex-wrap: wrap;
	gap: 10px;
}

.switch-button.is-active {
	background: var(--accent-soft);
	border-color: rgba(123, 42, 18, 0.42);
	color: var(--accent-strong);
}

.explanation-box,
.lab-output,
.step-card,
.quiz-result {
	padding: 18px;
	border-radius: 16px;
	background: rgba(255, 247, 239, 0.95);
	border: 1px solid rgba(68, 47, 24, 0.1);
}

.step-count {
	margin: 0 0 8px;
	color: var(--muted);
	font-weight: 700;
}

.lab-output code {
	font-family: var(--mono);
}

.flashcard-grid {
	grid-template-columns: repeat(4, minmax(0, 1fr));
}

.flashcard {
	position: relative;
	min-height: 180px;
	padding: 0;
	border-radius: 18px;
	overflow: hidden;
	perspective: 1000px;
	background: transparent;
	border: none;
}

.flashcard .face {
	position: absolute;
	inset: 0;
	display: grid;
	place-items: center;
	text-align: center;
	padding: 18px;
	border-radius: 18px;
	backface-visibility: hidden;
	transition: transform 0.4s ease;
	box-shadow: var(--shadow);
}

.flashcard .front {
	background: linear-gradient(180deg, #fff5ea, #fce6d2);
	font-family: var(--serif);
	font-size: 1.45rem;
}

.flashcard .back {
	background: linear-gradient(180deg, #29211c, #181210);
	color: #fff3e2;
	transform: rotateY(180deg);
	line-height: 1.6;
}

.flashcard.is-flipped .front {
	transform: rotateY(180deg);
}

.flashcard.is-flipped .back {
	transform: rotateY(360deg);
}

.exercise + .exercise {
	margin-top: 16px;
}

.hidden {
	display: none;
}

.quiz-form {
	display: grid;
	gap: 18px;
	margin-top: 12px;
}

.quiz-question {
	padding: 16px;
	border-radius: 16px;
	background: rgba(255, 251, 246, 0.92);
	border: 1px solid rgba(68, 47, 24, 0.1);
}

.quiz-question legend {
	font-weight: 700;
	margin-bottom: 12px;
}

.quiz-option {
	display: flex;
	align-items: flex-start;
	gap: 10px;
	padding: 8px 0;
}

.quiz-option input {
	margin-top: 4px;
	accent-color: var(--accent);
}

.quiz-result.is-good {
	border-color: rgba(15, 111, 82, 0.34);
	background: rgba(228, 248, 240, 0.9);
}

.quiz-result.is-mid {
	border-color: rgba(140, 90, 19, 0.34);
	background: rgba(255, 245, 224, 0.95);
}

.quiz-result.is-bad {
	border-color: rgba(173, 67, 37, 0.34);
	background: rgba(255, 234, 229, 0.95);
}

@media (max-width: 1100px) {
	.page-shell {
		grid-template-columns: 1fr;
	}

	.sidebar {
		position: static;
		max-height: none;
	}

	.two-column,
	.three-column,
	.interactive-grid,
	.flashcard-grid {
		grid-template-columns: 1fr;
	}
}

@media (max-width: 720px) {
	.page-shell {
		padding: 16px;
		gap: 18px;
	}

	.sidebar,
	.lesson {
		padding: 18px;
	}

	.lesson-top,
	.card-head,
	.panel-head {
		flex-direction: column;
		align-items: flex-start;
	}

	.button-row {
		width: 100%;
	}

	button {
		width: 100%;
	}
}