/* Dán và thay thế toàn bộ nội dung của tệp style.css */

/* --- Google Fonts Import --- */
@import url('https://fonts.googleapis.com/css2?family=Manrope:wght@400;500;600;700&display=swap');

/* --- Color Palette & Root Variables --- */
:root {
    --font-family-main: 'Manrope', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    
    --primary-color: #4A90E2;      /* A calming, professional blue */
    --primary-color-light: #EAF2FB; /* Light blue for highlights/backgrounds */
    --success-color: #50C878;      /* A softer, modern green */
    --danger-color: #E57373;       /* A less aggressive red */
    --warning-color: #FFB74D;      /* A gentle orange */
    --select-color: #F39C12;       /* A distinct orange for selection */

    --text-color-dark: #2D3748;    /* Dark gray for headings and main text */
    --text-color-medium: #4A5568;  /* Medium gray for secondary text */
    --text-color-light: #718096;   /* Light gray for placeholders/labels */
    
    --bg-color-main: #F7FAFC;      /* Very light gray background */
    --bg-color-paper: #FFFFFF;     /* White for the main workspace */
    --border-color: #E2E8F0;       /* Light gray for borders */

    --shadow-color: rgba(0, 0, 0, 0.05);
    --border-radius-md: 8px;
    --border-radius-sm: 5px;
    --transition-speed: 0.2s;
}

/* --- Global Styles --- */
*, *::before, *::after {
    box-sizing: border-box;
}

body {
    font-family: var(--font-family-main);
    background-color: var(--bg-color-main);
    color: var(--text-color-medium);
    margin: 0;
    padding: 24px;
    display: flex;
    flex-direction: column;
    align-items: center;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* --- Header & Title Input --- */
.header-container {
    width: 100%;
    max-width: 1100px;
    margin-bottom: 24px;
}
#exercise-title {
    width: 100%;
    padding: 12px 20px;
    font-size: 28px;
    font-weight: 700;
    color: var(--text-color-dark);
    border: 2px solid transparent;
    border-radius: var(--border-radius-md);
    text-align: center;
    background-color: var(--bg-color-paper);
    transition: border-color var(--transition-speed), box-shadow var(--transition-speed);
}
#exercise-title:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px var(--primary-color-light);
    outline: none;
}
#exercise-title.missing {
    border-color: var(--danger-color);
}
#exercise-title::placeholder {
    color: #A0AEC0;
    font-weight: 600;
}


/* --- Main Container --- */
.container { 
    width: 100%; 
    max-width: 1100px; 
    background: var(--bg-color-paper); 
    border-radius: var(--border-radius-md); 
    border: 1px solid var(--border-color);
    box-shadow: 0 4px 12px var(--shadow-color); 
}

/* --- Controls Panel --- */
.controls { 
    padding: 12px 20px; 
    background-color: #FFFFFF; 
    border-bottom: 1px solid var(--border-color); 
    display: flex; 
    align-items: center; 
    flex-wrap: wrap; 
    gap: 12px;
    position: sticky;
    top: 0;
    z-index: 100;
    border-top-left-radius: var(--border-radius-md);
    border-top-right-radius: var(--border-radius-md);
}

.controls label {
    font-weight: 600;
    color: var(--text-color-light);
    font-size: 14px;
    margin-right: -4px;
}
.divider {
    width: 1px;
    height: 24px;
    background-color: var(--border-color);
    margin: 0 8px;
}
.tool-btn {
    padding: 6px 12px;
    border: 1px solid var(--border-color);
    background-color: #FFFFFF;
    color: var(--text-color-medium);
    border-radius: var(--border-radius-sm);
    cursor: pointer;
    font-size: 16px;
    font-weight: 500;
    min-width: 40px;
    text-align: center;
    transition: all var(--transition-speed) ease;
    display: inline-flex;
    align-items: center;
    justify-content: center;
}
.tool-btn.icon-btn {
    font-size: 22px;
    font-weight: bold;
    padding: 2px 10px; /* Adjust padding for bigger font */
}
.tool-btn:hover {
    background-color: var(--bg-color-main);
    border-color: #CBD5E0;
}
.tool-btn.active-draw {
    background-color: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
}
.tool-btn.active-select {
    background-color: var(--select-color);
    color: white;
    border-color: var(--select-color);
}
.tool-btn.toggled-on {
    background-color: var(--primary-color-light);
    color: var(--primary-color);
    border-color: var(--primary-color);
}

#undo-btn { background-color: var(--warning-color); border-color: var(--warning-color); color: white; }
#undo-btn:hover { background-color: #FFA726; }

#help-btn { background-color: transparent; border-color: var(--border-color); color: var(--text-color-medium); }
#help-btn:hover { background-color: var(--bg-color-main); color: var(--primary-color); }

#color-picker {
    width: 36px; height: 36px; padding: 2px;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-sm);
    background-color: transparent; cursor: pointer;
}

#export-pdf-btn {
    background-color: var(--success-color);
    border-color: var(--success-color);
    color: white;
    font-weight: 600;
    margin-left: auto; /* Push to the far right */
}
#export-pdf-btn:hover {
    background-color: #47B96C;
    border-color: #47B96C;
}

/* --- Timer --- */
.timer-container {
    padding: 12px 20px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    border-bottom: 1px solid var(--border-color);
    background: #FDFDFD;
}
#timer-display {
    font-size: 24px;
    font-weight: 700;
    font-family: 'Courier New', Courier, monospace;
    color: var(--text-color-dark);
}
.timer-controls {
    display: flex;
    align-items: center;
    gap: 8px;
}
#timer-input {
    width: 70px;
    padding: 6px 10px;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-sm);
    background-color: #FFFFFF;
}
#timer-input:focus {
    border-color: var(--primary-color);
    outline: none;
}

.timer-controls button {
    padding: 6px 12px;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-sm);
    cursor: pointer;
    background-color: #FFFFFF;
    font-weight: 500;
}
.timer-controls button:hover {
    background-color: var(--bg-color-main);
}
#start-timer-btn {
    background-color: var(--primary-color-light);
    color: var(--primary-color);
    border-color: var(--primary-color-light);
}


/* --- Workspace & Sections --- */
.workspace {
    display: flex; flex-direction: column;
    padding: 24px; gap: 0; 
}
.multiple-choice-section, .essay-section {
    position: relative;
    padding: 20px;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-md);
    transition: border-color var(--transition-speed), box-shadow var(--transition-speed);
    cursor: pointer;
    background-color: #FFFFFF;
    margin-bottom: 32px; 
}
.multiple-choice-section.selected, .essay-section.selected {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px var(--primary-color-light);
}
.section-header {
    display: flex; justify-content: space-between; align-items: center;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 12px; margin-bottom: 16px;
}
.section-header h2 {
    margin: 0; padding: 0; border: none;
    font-size: 18px;
    font-weight: 600;
    color: var(--text-color-dark);
}
.delete-btn {
    background: none; border: none; font-size: 20px; cursor: pointer;
    color: var(--text-color-light); transition: all var(--transition-speed); padding: 5px;
}
.delete-btn:hover { color: var(--danger-color); transform: scale(1.1); }

/* --- Image Area --- */
.image-container {
    position: relative;
    width: 100%;
    min-height: 250px;
    border: 2px dashed var(--border-color);
    border-radius: var(--border-radius-md);
    display: flex;
    justify-content: center; align-items: center;
    background-color: var(--bg-color-main);
    transition: border-color var(--transition-speed);
    resize: vertical; overflow: auto;
    max-width: 100%;
    margin-left: auto;
    margin-right: auto;
}
.image-container.has-image {
    border: 1px solid var(--border-color);
    background-color: #FFFFFF;
}
.placeholder-content {
    color: var(--text-color-light); text-align: center;
    display: flex; flex-direction: column; align-items: center; gap: 12px;
}
.placeholder-icon { color: #CBD5E0; }
.upload-btn-local {
    font-size: 14px; padding: 8px 14px;
    background-color: #FFFFFF;
    border: 1px solid var(--border-color);
    color: var(--text-color-medium);
}
.exam-image {
    max-width: 100%;
    border-radius: var(--border-radius-sm);
    display: none;
    position: relative;
    z-index: 1;
    /* *** NEW: Blend mode for transparent background *** */
    mix-blend-mode: multiply;
}
.image-container.has-image .exam-image { display: block; }
.image-container.has-image .placeholder-content { display: none; }

.drawing-canvas, .ruler-canvas { position: absolute; top: 0; left: 0; pointer-events: none; z-index: 2; }
.drawing-canvas.active, .ruler-canvas.active { pointer-events: auto; }

/* --- Essay Section --- */
.essay-container { 
    position: relative; 
    color: var(--text-color-dark); /* Màu chữ mặc định */
}

.essay-render-target, .essay-textarea {
    width: 100%;
    min-height: 150px;
    border: 1px solid var(--border-color);
    padding: 16px;
    font-size: 18px; 
    line-height: 1.8;
    background-image: linear-gradient(to bottom, #EDF2F7 1px, transparent 1px);
    background-size: 100% calc(1.8em + 0.4px);
    background-attachment: local;
    outline: none;
    border-radius: var(--border-radius-md);
    color: inherit; /* SỬA LỖI: Kế thừa màu từ .essay-container */
    word-wrap: break-word;
    white-space: pre-wrap; 
}

.essay-textarea {
    resize: none; 
    overflow-y: hidden;
}

.essay-render-target {
    min-height: calc(1.8em + 32px);
}

/* Trạng thái xem trước (mặc định) */
.essay-section .essay-textarea {
    display: none;
}
.essay-section .essay-render-target {
    display: block;
}

/* Trạng thái soạn thảo */
.essay-section.editing .essay-textarea {
    display: block;
}
.essay-section.editing .essay-render-target {
    display: none;
}

.essay-textarea:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px var(--primary-color-light);
}


/* --- Section Inserter --- */
.section-inserter {
    position: absolute;
    bottom: -32px; 
    left: 0;
    width: 100%;
    height: 32px;
    display: flex;
    justify-content: center;
    align-items: center;
    opacity: 0; 
    transition: opacity var(--transition-speed) ease-in-out;
}
.multiple-choice-section:hover + .multiple-choice-section .section-inserter,
.multiple-choice-section:hover + .essay-section .section-inserter,
.essay-section:hover + .multiple-choice-section .section-inserter,
.essay-section:hover + .essay-section .section-inserter,
.multiple-choice-section:hover .section-inserter,
.essay-section:hover .section-inserter,
.workspace > div:last-child:hover .section-inserter {
    opacity: 1; 
}
.section-inserter .inserter-line {
    width: 100%;
    height: 1px;
    background: var(--border-color);
    position: absolute;
    top: 50%;
    z-index: 1;
}
.inserter-btn-main {
    position: relative;
    z-index: 2;
    width: 30px;
    height: 30px;
    border-radius: 50%;
    border: 1px solid var(--border-color);
    background: var(--bg-color-paper);
    cursor: pointer;
    font-size: 18px;
    color: var(--primary-color);
    display: flex;
    justify-content: center;
    align-items: center;
    box-shadow: 0 2px 5px var(--shadow-color);
    transition: all var(--transition-speed) ease;
}
.inserter-btn-main:hover {
    transform: scale(1.1);
    background-color: var(--primary-color-light);
}
.inserter-options {
    position: absolute;
    z-index: 3;
    display: flex;
    gap: 10px;
    background-color: var(--bg-color-paper);
    padding: 8px;
    border-radius: var(--border-radius-md);
    box-shadow: 0 4px 12px rgba(0,0,0,0.1);
    transform: translateY(-10px) scale(0.95);
    opacity: 0;
    visibility: hidden;
    transition: all var(--transition-speed) ease;
    pointer-events: none;
}
.section-inserter.active .inserter-options {
    transform: translateY(0) scale(1);
    opacity: 1;
    visibility: visible;
    pointer-events: auto;
}
.section-inserter.active .inserter-btn-main {
    opacity: 0;
    pointer-events: none;
}
.inserter-option-btn {
    padding: 8px 16px;
    border: 1px solid var(--border-color);
    background-color: #FFFFFF;
    color: var(--text-color-medium);
    border-radius: var(--border-radius-sm);
    cursor: pointer;
    font-size: 14px;
    font-weight: 600;
    white-space: nowrap;
}
.inserter-option-btn:hover {
    background-color: var(--primary-color-light);
    border-color: var(--primary-color);
    color: var(--primary-color);
}


/* --- Modals & Overlays --- */
.modal-overlay {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%;
    background-color: rgba(30, 41, 59, 0.6);
    display: none; justify-content: center; align-items: center;
    z-index: 1000;
    backdrop-filter: blur(4px);
}
.modal-overlay.visible { display: flex; }
.modal-content {
    background: white; padding: 24px 32px;
    border-radius: var(--border-radius-md);
    box-shadow: 0 10px 25px rgba(0,0,0,0.1);
    text-align: center;
    position: relative;
    max-width: 80%;
}
.modal-content p { margin: 8px 0 24px; font-size: 16px; color: var(--text-color-medium); }
.modal-actions { display: flex; gap: 12px; justify-content: center; }
.modal-btn {
    padding: 10px 20px; border: none; border-radius: var(--border-radius-sm);
    font-size: 15px; font-weight: 600; cursor: pointer;
    transition: opacity var(--transition-speed);
}
.modal-btn:hover { opacity: 0.9; }
.modal-btn.confirm { background-color: var(--danger-color); color: white; }
.modal-btn.cancel { background-color: var(--border-color); color: var(--text-color-medium); }

.help-content { 
    text-align: left; 
    max-height: 85vh; 
    overflow-y: auto; 
}
.help-content h2 { margin-top: 0; margin-bottom: 24px; color: var(--text-color-dark); }
.help-content h4 {
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 8px; margin-top: 24px; margin-bottom: 12px;
    color: var(--text-color-dark); font-weight: 600;
}
.help-content ul { padding-left: 20px; }
.help-content ul li { margin-bottom: 10px; }
.close-btn {
    position: absolute; top: 12px; right: 16px;
    font-size: 28px; font-weight: bold; color: #A0AEC0;
    cursor: pointer;
}
.close-btn:hover { color: var(--text-color-dark); }


/* --- Lock State & Gamified Overlay --- */
#lock-overlay {
    position: fixed; top: 0; left: 0;
    width: 100%; height: 100%;
    background-color: rgba(247, 250, 252, 0.85);
    z-index: 999;
    display: none; justify-content: center; align-items: center;
    backdrop-filter: blur(3px);
    text-align: center;
}
#lock-overlay.visible { display: flex; }

#overlay-content {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 20px;
    background-color: rgba(255, 255, 255, 0.95);
    padding: 30px 40px;
    border-radius: var(--border-radius-md);
    box-shadow: 0 5px 20px rgba(0,0,0,0.08);
}
#overlay-text {
    margin: 0;
    font-size: 20px; 
    font-weight: 600; 
    color: var(--text-color-dark);
}
.spinner {
    width: 40px;
    height: 40px;
    border: 4px solid var(--border-color);
    border-top-color: var(--primary-color);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}
#lock-overlay.finished .spinner {
    display: none;
}
@keyframes spin {
    to { transform: rotate(360deg); }
}

body.locked .controls,
body.locked .workspace,
body.locked .timer-controls {
    pointer-events: none;
    opacity: 0.7;
}

#image-input-hidden { display: none; }
.temp-text-input { position: absolute; border: 1px dashed var(--primary-color); outline: none; z-index: 100; padding: 2px 4px; }