@font-face {
  font-family: 'KaTeX_Main_Minus';
  src: url('https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/fonts/KaTeX_Main-Regular.woff2') format('woff2'),
       url('https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/fonts/KaTeX_Main-Regular.woff') format('woff'),
       url('https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/fonts/KaTeX_Main-Regular.ttf') format('truetype');
  font-weight: 100 900;
  font-style: normal;
  unicode-range: U+2212;
}

@font-face {
  font-family: 'KaTeX_Math_X';
  src: url('https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/fonts/KaTeX_Math-Italic.woff2') format('woff2'),
       url('https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/fonts/KaTeX_Math-Italic.woff') format('woff'),
       url('https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/fonts/KaTeX_Math-Italic.ttf') format('truetype');
  font-weight: normal;
  font-style: normal;
  unicode-range: U+0078, U+0058, U+0079, U+0059;
}

:root {
    --primary-color: #4F46E5;
    --primary-hover: #4338CA;
    --success-color: #10B981;
    --error-color: #EF4444;
    --text-main: #1F2937;
    --text-muted: #6B7280;
    --bg-card: rgba(255, 255, 255, 0.85);
    --border-card: rgba(255, 255, 255, 0.4);
}

.exercise-wrapper {
    font-family: 'Inter', sans-serif;
    color: var(--text-main);
    display: flex;
    justify-content: center;
    align-items: center;
    position: relative;
    border-radius: 12px;
    padding: 15px 20px;
    overflow: hidden;
}

.app-container {
    width: 100%;
    max-width: 700px;
    padding: 0px 10px 10px 10px;
    display: flex;
    flex-direction: column;
    gap: 15px;
}

.app-header {
    text-align: center;
}

.glass-card {
    background: var(--bg-card);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border: 1px solid var(--border-card);
    border-radius: 20px;
    padding: 18px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.05), inset 0 1px 0 rgba(255, 255, 255, 0.6);
    display: flex;
    flex-direction: column;
    gap: 18px;
}

.exercise-section {
    background: white;
    padding: 12px;
    border-radius: 12px;
    text-align: center;
    box-shadow: inset 0 2px 4px rgba(0,0,0,0.02);
    border: 1px solid #E5E7EB;
}

.math-display {
    font-size: 1.4rem;
    color: var(--text-main);
    margin: 4px 0;
}

/* Canvas container */
#canvas-container {
    width: 100%;
    max-width: 400px;
    aspect-ratio: 1 / 1;
    margin: 8px auto;
    background: #ffffff;
    border: 2px solid #9CA3AF;
    border-radius: 12px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.06);
    overflow: hidden;
    position: relative;
    touch-action: none;
}

#graphCanvas {
    width: 100%;
    height: 100%;
    display: block;
    background: #ffffff;
    cursor: zoom-in;
    transition: transform 0.3s ease-out;
    transform-origin: center;
    touch-action: none;
}

/* Input Section */
.input-section {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 10px;
    width: 100%;
}

.input-container-row {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    font-size: 1.3rem;
    font-weight: 600;
    color: #1F2937;
    width: 100%;
}

#answer-input {
    width: 100%;
    max-width: 280px;
    text-align: center;
    padding: 8px 14px;
    font-size: 1.25rem;
    font-family: 'KaTeX_Math_X', 'KaTeX_Main_Minus', 'Inter', sans-serif;
    font-weight: 600;
    letter-spacing: 1px;
    border: 2px solid #D1D5DB;
    border-radius: 10px;
    outline: none;
    transition: all 0.2s ease;
    background: #ffffff;
    color: #1F2937;
}

#answer-input:focus, #answer-input.active-input {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 4px rgba(79, 70, 229, 0.15);
}

.btn {
    padding: 8px 20px;
    font-size: 1.1rem;
    font-weight: 600;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.2s ease;
    font-family: 'Inter', sans-serif;
}

.primary-btn {
    background: var(--primary-color);
    color: white;
    box-shadow: 0 4px 6px rgba(79, 70, 229, 0.2);
}

.primary-btn:hover {
    background: var(--primary-hover);
    transform: translateY(-1px);
    box-shadow: 0 6px 12px rgba(79, 70, 229, 0.25);
}

.primary-btn:active {
    transform: translateY(1px);
}

.btn:disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

.secondary-btn {
    background: #F3F4F6;
    color: var(--text-main);
    border: 1px solid #E5E7EB;
}

.secondary-btn:hover {
    background: #E5E7EB;
}

/* Feedback Section */
.feedback {
    padding: 12px 20px;
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
    font-weight: 600;
    font-size: 1rem;
    animation: fadeIn 0.3s ease;
    margin: 8px auto;
    width: 100%;
    text-align: center;
}

.feedback.success {
    background: rgba(16, 185, 129, 0.95);
    color: #ffffff;
    border: 1px solid rgba(16, 185, 129, 1);
}

.feedback.error {
    background: rgba(239, 68, 68, 0.95);
    color: #ffffff;
    border: 1px solid rgba(239, 68, 68, 1);
}

.feedback.warning {
    background: #FEF3C7;
    color: #92400E;
    border: 1px solid #F59E0B;
}

.hidden {
    display: none !important;
}

/* Animations */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(-5px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Virtual Keyboard */
.virtual-keyboard {
    display: grid;
    grid-template-columns: repeat(7, 1fr);
    gap: 4px;
    background: rgba(255, 255, 255, 0.95);
    padding: 6px;
    border-radius: 10px;
    border: 1px solid #E5E7EB;
    box-shadow: 0 4px 15px rgba(0,0,0,0.05);
    max-width: 340px;
    margin: 4px auto;
    width: 100%;
}

.vk-btn {
    padding: 5px 0;
    min-height: 36px;
    font-size: 1.1rem;
    font-weight: 600;
    border: 1px solid #E5E7EB;
    border-radius: 6px;
    background: #F9FAFB;
    color: var(--text-main);
    cursor: pointer;
    transition: all 0.1s ease;
    font-family: 'KaTeX_Math_X', 'KaTeX_Main_Minus', 'Inter', sans-serif;
    display: flex;
    align-items: center;
    justify-content: center;
    user-select: none;
    -webkit-tap-highlight-color: transparent;
}

.vk-btn:hover:not(:disabled) {
    background: #E5E7EB;
}

.vk-btn:active:not(:disabled) {
    background: #D1D5DB;
    transform: scale(0.96);
}

.vk-btn:disabled {
    opacity: 0.25;
    cursor: not-allowed;
    background: #F3F4F6;
    color: #9CA3AF;
    box-shadow: none;
    transform: none !important;
}

.vk-var {
    color: #7C3AED;
    font-size: 1.25rem;
    font-weight: 700;
    font-style: italic;
    background: #F5F3FF;
    border-color: #DDD6FE;
}

.vk-var:hover:not(:disabled) {
    background: #EDE9FE;
}

.vk-op {
    color: #4F46E5;
    font-size: 1.2rem;
    font-weight: bold;
}

.vk-minus {
    font-size: 1.3rem;
    line-height: 1;
}

.vk-del {
    background: #FEE2E2;
    color: #DC2626;
    border-color: #FCA5A5;
}

.vk-del:hover:not(:disabled) {
    background: #FCA5A5;
}

/* Responsive Adjustments */
@media (max-width: 640px) {
    .exercise-wrapper {
        padding: 8px 4px;
    }

    .app-container {
        padding: 0 4px 5px 4px;
        gap: 10px;
    }

    .glass-card {
        padding: 12px 8px;
        gap: 12px;
    }
    
    #canvas-container {
        max-width: 320px;
    }

    .virtual-keyboard {
        gap: 3px;
        padding: 5px;
        max-width: 300px;
    }

    .vk-btn {
        padding: 4px 0;
        min-height: 32px;
        font-size: 1rem;
    }

    .vk-op {
        font-size: 1.1rem;
    }
}

.blue-btn {
    background-color: #3B82F6 !important;
    color: white !important;
    width: fit-content !important;
    margin: 0 auto !important;
    display: block;
    padding: 0.6rem 1.8rem !important;
    border-radius: 10px !important;
    font-weight: 600 !important;
    box-shadow: 0 4px 6px rgba(59, 130, 246, 0.25) !important;
    transition: all 0.2s ease !important;
}

.blue-btn:hover {
    background-color: #2563EB !important;
    transform: translateY(-1px) !important;
}