:root {
    --board-green: #1F3A34;
    --board-green-light: #2C4F47;
    --paper: #FAF6EB;
    --paper-line: #E4DCC8;
    --margin-red: #C15B4A;
    --chalk-yellow: #E8C468;
    --ink: #2A2A26;
    --ink-soft: #6B6558;
    --error-red: #B0453A;
}

* { box-sizing: border-box; }

body {
    margin: 0;
    background: var(--paper);
    color: var(--ink);
    font-family: 'Hind Siliguri', sans-serif;
    min-height: 100vh;
}

h1, .solve-btn, .mode-btn { font-family: 'Baloo Da 2', 'Hind Siliguri', sans-serif; }

/* ---------- Header ---------- */
.app-header {
    background: var(--board-green);
    color: var(--paper);
    padding: 28px 20px 22px;
    border-bottom: 4px solid var(--chalk-yellow);
}
.header-inner {
    display: flex;
    align-items: center;
    gap: 10px;
    max-width: 520px;
    margin: 0 auto;
}
.chalk-icon { font-size: 26px; }
.app-header h1 {
    margin: 0;
    font-size: 24px;
    font-weight: 700;
    letter-spacing: 0.5px;
}
.tagline {
    max-width: 520px;
    margin: 8px auto 0;
    font-size: 14px;
    color: #CFE0DA;
}

/* ---------- Notebook page ---------- */
.notebook {
    max-width: 520px;
    margin: 20px auto;
    padding: 20px 20px 20px 28px;
    background:
        linear-gradient(var(--paper) 0, var(--paper) 100%),
        repeating-linear-gradient(var(--paper) 0px, var(--paper) 30px, var(--paper-line) 31px);
    border-left: 3px solid var(--margin-red);
    position: relative;
}

/* ---------- Mode toggle ---------- */
.mode-toggle {
    display: flex;
    gap: 8px;
    margin-bottom: 16px;
}
.mode-btn {
    flex: 1;
    padding: 10px;
    border: 2px solid var(--board-green);
    background: transparent;
    color: var(--board-green);
    border-radius: 10px;
    font-size: 15px;
    font-weight: 600;
    cursor: pointer;
}
.mode-btn.active {
    background: var(--board-green);
    color: var(--paper);
}

/* ---------- Input panels ---------- */
.input-panel.hidden { display: none; }

textarea {
    width: 100%;
    padding: 14px;
    font-size: 16px;
    font-family: 'Hind Siliguri', sans-serif;
    border: 2px solid var(--paper-line);
    border-radius: 10px;
    background: #fff;
    resize: vertical;
}
textarea:focus { outline: none; border-color: var(--board-green); }

.upload-box {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 8px;
    padding: 32px 16px;
    border: 2px dashed var(--board-green-light);
    border-radius: 12px;
    background: #fff;
    cursor: pointer;
    text-align: center;
}
.upload-icon { font-size: 34px; }
#uploadLabel { color: var(--ink-soft); font-size: 15px; }

.preview-img {
    display: block;
    width: 100%;
    margin-top: 12px;
    border-radius: 10px;
    border: 2px solid var(--paper-line);
}
.preview-img.hidden { display: none; }

/* ---------- Solve button ---------- */
.solve-btn {
    width: 100%;
    margin-top: 16px;
    padding: 14px;
    font-size: 17px;
    font-weight: 700;
    color: var(--board-green);
    background: var(--chalk-yellow);
    border: none;
    border-radius: 10px;
    cursor: pointer;
}
.solve-btn:active { transform: translateY(1px); }
.solve-btn:disabled { opacity: 0.6; cursor: not-allowed; }

/* ---------- Loading ---------- */
.loading-box {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-top: 18px;
    color: var(--ink-soft);
    font-size: 15px;
}
.loading-box.hidden { display: none; }
.spinner {
    width: 18px; height: 18px;
    border: 3px solid var(--paper-line);
    border-top-color: var(--board-green);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* ---------- Error ---------- */
.error-box {
    margin-top: 16px;
    padding: 12px 14px;
    background: #FBEAE7;
    border-left: 4px solid var(--error-red);
    border-radius: 6px;
    color: var(--error-red);
    font-size: 14px;
}
.error-box.hidden { display: none; }

/* ---------- Solution ---------- */
.solution-box {
    margin-top: 22px;
    padding: 18px;
    background: #fff;
    border-radius: 12px;
    border: 1px solid var(--paper-line);
    box-shadow: 0 2px 0 var(--paper-line);
}
.solution-box.hidden { display: none; }
#solutionContent { font-size: 16px; line-height: 1.75; }
#solutionContent strong { color: var(--board-green); }

.simplify-btn {
    margin-top: 16px;
    width: 100%;
    padding: 11px;
    background: transparent;
    border: 2px solid var(--board-green);
    color: var(--board-green);
    border-radius: 10px;
    font-size: 14px;
    font-weight: 600;
    cursor: pointer;
}
.simplify-btn.hidden { display: none; }

/* ---------- Correction panel ---------- */
.correction-panel { margin-top: 18px; padding-top: 16px; border-top: 1px dashed var(--paper-line); }
.correction-panel.hidden { display: none; }
.correction-label {
    display: block;
    font-size: 13px;
    color: var(--ink-soft);
    margin-bottom: 6px;
}
#correctedProblem {
    width: 100%;
    padding: 10px;
    font-size: 15px;
    font-family: 'Hind Siliguri', sans-serif;
    border: 2px solid var(--paper-line);
    border-radius: 8px;
    resize: vertical;
}
#correctedProblem:focus { outline: none; border-color: var(--board-green); }
.correction-btn {
    margin-top: 10px;
    width: 100%;
    padding: 11px;
    background: transparent;
    border: 2px solid var(--margin-red);
    color: var(--margin-red);
    border-radius: 10px;
    font-size: 14px;
    font-weight: 600;
    cursor: pointer;
}

/* ---------- History ---------- */
.history-section { margin-top: 26px; }
.history-toggle {
    background: none;
    border: none;
    color: var(--ink-soft);
    font-size: 14px;
    cursor: pointer;
    padding: 0;
}
.history-list { margin-top: 12px; }
.history-list.hidden { display: none; }
.history-item {
    padding: 10px 0;
    border-bottom: 1px solid var(--paper-line);
    font-size: 14px;
    color: var(--ink-soft);
    cursor: pointer;
}
.history-item:hover { color: var(--ink); }

/* ---------- Crop UI ---------- */
.crop-stage.hidden { display: none; }
.crop-stage { margin-top: 14px; }
.crop-hint {
    font-size: 13px;
    color: var(--ink-soft);
    margin: 0 0 10px;
}
.crop-image-wrap {
    position: relative;
    max-width: 100%;
    line-height: 0;
    touch-action: none;
    border-radius: 8px;
    overflow: hidden;
    background: #000;
}
.crop-image-wrap img {
    display: block;
    width: 100%;
    height: auto;
    user-select: none;
    -webkit-user-drag: none;
}
.crop-box {
    position: absolute;
    border: 2px solid var(--chalk-yellow);
    box-shadow: 0 0 0 9999px rgba(0, 0, 0, 0.55);
    cursor: move;
    touch-action: none;
}
.crop-handle {
    position: absolute;
    width: 22px;
    height: 22px;
    background: var(--chalk-yellow);
    border-radius: 50%;
    border: 2px solid var(--board-green);
    touch-action: none;
}
.crop-handle.tl { top: -11px; left: -11px; cursor: nwse-resize; }
.crop-handle.tr { top: -11px; right: -11px; cursor: nesw-resize; }
.crop-handle.bl { bottom: -11px; left: -11px; cursor: nesw-resize; }
.crop-handle.br { bottom: -11px; right: -11px; cursor: nwse-resize; }

.crop-actions {
    display: flex;
    gap: 8px;
    margin-top: 12px;
}
.crop-confirm-btn, .crop-skip-btn {
    flex: 1;
    padding: 12px;
    border-radius: 10px;
    font-size: 14px;
    font-weight: 600;
    cursor: pointer;
}
.crop-confirm-btn {
    background: var(--chalk-yellow);
    color: var(--board-green);
    border: none;
}
.crop-skip-btn {
    background: transparent;
    color: var(--ink-soft);
    border: 2px solid var(--paper-line);
}

/* ---------- Footer ---------- */
.app-footer {
    text-align: center;
    color: var(--ink-soft);
    font-size: 12px;
    padding: 24px 0 32px;
}

@media (min-width: 560px) {
    .app-header h1 { font-size: 28px; }
}