.fourier-lab {
    margin: 1.4rem 0 1.6rem;
    border: 1px solid var(--border);
    border-radius: 1rem;
    background: linear-gradient(165deg, var(--card-top), var(--card-bottom));
    box-shadow: var(--shadow);
    overflow: hidden;
}

.fourier-lab-head {
    padding: 1rem 1.1rem .75rem;
    border-bottom: 1px solid var(--border);
}

.fourier-lab-head h3 {
    margin: 0 0 .35rem;
    font-size: 1.15rem;
    color: var(--article-strong);
}

.fourier-lab-head p {
    margin: 0;
    color: var(--article-byline);
    font-size: .92rem;
}

.fourier-lab-body {
    padding: 1rem 1.1rem 1.2rem;
    display: grid;
    gap: 1rem;
}

.fourier-controls {
    display: grid;
    gap: .85rem;
}

.fourier-row {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
    gap: .75rem;
}

.fourier-field label {
    display: block;
    font-size: .82rem;
    font-weight: 700;
    color: var(--article-strong);
    margin-bottom: .3rem;
}

.fourier-field select,
.fourier-field input[type="number"],
.fourier-field input[type="text"],
.fourier-field textarea {
    width: 100%;
    border: 1px solid var(--border);
    border-radius: .55rem;
    background: var(--table-surface);
    color: var(--article-text);
    padding: .45rem .6rem;
    font: inherit;
}

.fourier-field textarea {
    min-height: 4.2rem;
    resize: vertical;
    font-family: ui-monospace, Consolas, monospace;
    font-size: .85rem;
}

.fourier-field input[type="range"] {
    width: 100%;
    accent-color: var(--accent-2, #30d5c8);
}

.fourier-hint {
    margin: .25rem 0 0;
    font-size: .78rem;
    color: var(--article-byline);
}

.fourier-actions {
    display: flex;
    flex-wrap: wrap;
    gap: .55rem;
}

.fourier-btn {
    border: 1px solid var(--border);
    border-radius: .65rem;
    background: var(--btn-muted-bg);
    color: var(--btn-muted-text);
    padding: .45rem .85rem;
    font: inherit;
    font-weight: 700;
    cursor: pointer;
}

.fourier-btn-primary {
    background: color-mix(in srgb, var(--accent-2) 28%, transparent);
    border-color: color-mix(in srgb, var(--accent-2) 55%, var(--border));
    color: var(--article-strong);
}

.fourier-plots {
    display: grid;
    gap: .85rem;
}

@media (min-width: 820px) {
    .fourier-plots {
        grid-template-columns: 1.15fr .85fr;
    }
}

.fourier-plot {
    border: 1px solid var(--border);
    border-radius: .85rem;
    background: rgba(0, 0, 0, .22);
    padding: .55rem .55rem .45rem;
}

[data-theme="light"] .fourier-plot {
    background: rgba(18, 20, 32, .05);
}

.fourier-plot h4 {
    margin: 0 0 .4rem;
    font-size: .88rem;
    color: var(--article-strong);
}

.fourier-plot canvas {
    display: block;
    width: 100%;
    height: 220px;
    border-radius: .45rem;
}

.fourier-plot p {
    margin: .4rem 0 0;
    font-size: .78rem;
    color: var(--article-byline);
}

.fourier-eq-box {
    border: 1px solid var(--border);
    border-radius: .75rem;
    padding: .7rem .85rem;
    background: var(--table-surface);
}

.fourier-eq-box .label {
    display: block;
    font-size: .72rem;
    letter-spacing: .04em;
    text-transform: uppercase;
    color: var(--article-byline);
    margin-bottom: .3rem;
}

.fourier-eq-box code {
    display: block;
    font-size: .86rem;
    color: var(--article-strong);
    word-break: break-word;
    line-height: 1.45;
}

.fourier-terms {
    width: 100%;
    border-collapse: collapse;
    font-size: .82rem;
}

.fourier-terms th,
.fourier-terms td {
    border: 1px solid var(--table-cell-border);
    padding: .35rem .45rem;
    text-align: center;
    color: var(--table-cell-text);
}

.fourier-terms th {
    background: var(--table-head-bg);
    color: var(--table-head-text);
}

.fourier-terms input {
    width: 100%;
    max-width: 5.5rem;
    border: 1px solid var(--border);
    border-radius: .35rem;
    background: transparent;
    color: inherit;
    padding: .2rem .3rem;
    text-align: center;
    font: inherit;
}

.fourier-warn {
    margin: 0;
    font-size: .82rem;
    color: var(--article-byline);
}

.fourier-toc {
    margin: 0 0 1.4rem;
    padding: .9rem 1rem 1rem;
    border: 1px solid var(--border);
    border-radius: .85rem;
    background: var(--table-surface);
    scroll-margin-top: 5rem;
}

.article h2[id],
#fourier-lab {
    scroll-margin-top: 5rem;
}

.fourier-toc-title {
    display: block;
    margin-bottom: .45rem;
    color: var(--article-strong);
    font-size: .95rem;
}

.fourier-toc-list {
    margin: 0;
    padding-left: 1.2rem;
    columns: 1;
    gap: 1.5rem;
}

@media (min-width: 720px) {
    .fourier-toc-list {
        columns: 2;
    }
}

.fourier-toc-list li {
    break-inside: avoid;
    margin: .2rem 0;
    color: var(--article-text);
    font-size: .9rem;
}

.fourier-toc-list a {
    color: var(--accent-2, #30d5c8);
    text-decoration: none;
}

.fourier-toc-list a:hover {
    text-decoration: underline;
}

.fourier-back {
    margin: .65rem 0 0;
    font-size: .85rem;
}

.fourier-back a {
    color: var(--accent-2, #30d5c8);
    text-decoration: none;
    font-weight: 600;
}

.fourier-back a:hover {
    text-decoration: underline;
}

.fourier-help {
    border: 1px solid var(--border);
    border-radius: .75rem;
    padding: .75rem .85rem;
    background: var(--table-surface);
}

.fourier-help h4 {
    margin: 0 0 .45rem;
    font-size: .95rem;
    color: var(--article-strong);
}

.fourier-help p {
    margin: 0 0 .35rem;
    font-size: .86rem;
    color: var(--article-text);
    line-height: 1.45;
}

.fourier-help p:last-child {
    margin-bottom: 0;
}

.fourier-demo-grid {
    display: grid;
    gap: .85rem;
    margin: 1rem 0 1.2rem;
}

@media (min-width: 720px) {
    .fourier-demo-grid {
        grid-template-columns: 1fr 1fr;
    }
}

.fourier-demo-grid .fourier-plot canvas {
    height: 180px;
}