body {
    margin: 0;
    padding: 0;
    background-color: var(--tg-theme-secondary-bg-color, #f0f2f5);
    color: var(--tg-theme-text-color, #222);
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    touch-action: none; /* iOS Safari rubber banding prevention */
}
#app-container {
    display: flex;
    flex-direction: column;
    height: 100vh;
    padding: 16px;
    box-sizing: border-box;
}
header {
    text-align: center;
    margin-bottom: 20px;
}
h1 {
    font-size: 24px;
    margin: 0 0 8px;
    background: linear-gradient(90deg, #4b6cb7 0%, #182848 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}
#subtitle {
    font-size: 14px;
    color: var(--tg-theme-hint-color, #888);
    margin: 0;
}
main {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
}
.canvas-wrapper {
    width: 100%;
    max-width: 400px;
    aspect-ratio: 1/1;
    background: #fff;
    border-radius: 16px;
    box-shadow: 0 8px 32px rgba(0,0,0,0.1);
    border: 2px solid var(--tg-theme-hint-color, #e1e1e1);
    position: relative;
    overflow: hidden;
}
canvas {
    width: 100%;
    height: 100%;
    display: block;
    cursor: crosshair;
}
.button-group {
    display: flex;
    gap: 12px;
    margin-top: 20px;
}
.btn {
    flex: 1;
    padding: 16px;
    border: none;
    border-radius: 12px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s;
    user-select: none;
}
.btn:active {
    transform: scale(0.96);
}
.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none;
}
.btn-primary {
    background-color: var(--tg-theme-button-color, #3498db);
    color: var(--tg-theme-button-text-color, #fff);
    box-shadow: 0 4px 12px rgba(52, 152, 219, 0.3);
}
.btn-secondary {
    background-color: transparent;
    border: 2px solid var(--tg-theme-button-color, #3498db);
    color: var(--tg-theme-button-color, #3498db);
}
/* Loading overlay */
#loadingOverlay {
    position: fixed;
    top: 0; left: 0; right: 0; bottom: 0;
    background: var(--tg-theme-bg-color, rgba(255, 255, 255, 0.8));
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    z-index: 999;
}
#loadingOverlay.hidden {
    display: none;
}
.spinner {
    width: 40px; height: 40px;
    border: 4px solid #f3f3f3;
    border-top: 4px solid var(--tg-theme-button-color, #3498db);
    border-radius: 50%;
    animation: spin 1s linear infinite;
    margin-bottom: 12px;
}
@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}