:root {
    /* Theme variables - Default Dark Mode */
    --bg-color: #0d0f14;
    --bg-gradient: radial-gradient(circle at 50% 50%, #1a1e29 0%, #0d0f14 100%);
    --text-color: #f3f4f6;
    --container-bg: rgba(26, 30, 41, 0.65);
    --container-border: rgba(255, 255, 255, 0.08);
    --container-shadow: 0 20px 40px rgba(0, 0, 0, 0.4), inset 0 1px 1px rgba(255, 255, 255, 0.1);
    
    --button-bg: #ffffff;
    --button-text: #0d0f14;
    --button-shadow: 0 4px 15px rgba(255, 255, 255, 0.15);
    --button-hover-shadow: 0 6px 25px rgba(255, 255, 255, 0.35);
    --button-hover-bg: #e2e8f0;
    
    --toggle-bg: rgba(255, 255, 255, 0.05);
    --toggle-border: rgba(255, 255, 255, 0.1);
    --toggle-color: #f3f4f6;
    --toggle-hover-bg: rgba(255, 255, 255, 0.15);
    
    --ball-border: rgba(255, 255, 255, 0.2);
    --ball-empty-bg: #1e293b;
    --ball-empty-border: rgba(255, 255, 255, 0.1);
    --ball-text: #ffffff;
    --ball-shadow: 0 4px 10px rgba(0, 0, 0, 0.3);
    
    --title-gradient: linear-gradient(135deg, #ff7272, #fbc400);
}

html[data-theme="light"] {
    /* Light Mode variables */
    --bg-color: #f8fafc;
    --bg-gradient: radial-gradient(circle at 50% 50%, #f1f5f9 0%, #e2e8f0 100%);
    --text-color: #0f172a;
    --container-bg: rgba(255, 255, 255, 0.85);
    --container-border: rgba(15, 23, 42, 0.06);
    --container-shadow: 0 20px 40px rgba(15, 23, 42, 0.08), inset 0 1px 0 rgba(255, 255, 255, 0.6);
    
    --button-bg: #0f172a;
    --button-text: #ffffff;
    --button-shadow: 0 4px 15px rgba(15, 23, 42, 0.2);
    --button-hover-shadow: 0 6px 25px rgba(15, 23, 42, 0.35);
    --button-hover-bg: #1e293b;
    
    --toggle-bg: rgba(15, 23, 42, 0.03);
    --toggle-border: rgba(15, 23, 42, 0.08);
    --toggle-color: #0f172a;
    --toggle-hover-bg: rgba(15, 23, 42, 0.08);
    
    --ball-border: rgba(15, 23, 42, 0.15);
    --ball-empty-bg: #f1f5f9;
    --ball-empty-border: rgba(15, 23, 42, 0.08);
    --ball-text: #0f172a;
    --ball-shadow: 0 4px 10px rgba(0, 0, 0, 0.06);
    
    --title-gradient: linear-gradient(135deg, #ff5e62, #ff9966);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    background: var(--bg-color);
    background-image: var(--bg-gradient);
    color: var(--text-color);
    transition: background 0.4s ease, color 0.4s ease;
    overflow-x: hidden;
    position: relative;
}

/* Elegant grid background texture */
body::before {
    content: "";
    position: absolute;
    inset: 0;
    width: 100%;
    height: 100%;
    background-image: radial-gradient(var(--toggle-border) 1px, transparent 1px);
    background-size: 24px 24px;
    opacity: 0.4;
    pointer-events: none;
    z-index: 0;
}

.container {
    text-align: center;
    position: relative;
    z-index: 1;
    background: var(--container-bg);
    border: 1px solid var(--container-border);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    padding: 3rem 2.5rem;
    border-radius: 24px;
    box-shadow: var(--container-shadow);
    max-width: 90%;
    width: 520px;
    transition: background 0.4s ease, border 0.4s ease, box-shadow 0.4s ease, transform 0.3s ease;
}

.container:hover {
    transform: translateY(-2px);
}

h1 {
    font-size: 2.5rem;
    font-weight: 800;
    letter-spacing: -1.5px;
    margin-top: 0;
    margin-bottom: 2.5rem;
    background: var(--title-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    text-fill-color: transparent;
}

.numbers-container {
    display: flex;
    justify-content: center;
    gap: 0.85rem;
    margin-bottom: 3rem;
    flex-wrap: wrap;
}

.number {
    width: 56px;
    height: 56px;
    border-radius: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.4rem;
    font-weight: 700;
    color: #ffffff; /* Numbers themselves look best on standard vivid bg */
    border: 2px solid var(--ball-border);
    background: var(--ball-empty-bg);
    box-shadow: var(--ball-shadow);
    transition: all 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    transform: scale(0.9);
}

/* Custom empty look when no number is generated */
.number:empty {
    border: 2px dashed var(--ball-empty-border);
    background: var(--ball-empty-bg);
    box-shadow: none;
}

.number:empty::after {
    content: "?";
    color: var(--text-color);
    opacity: 0.3;
    font-size: 1.2rem;
}

/* Scale up generated numbers */
.number:not(:empty) {
    transform: scale(1);
    animation: ball-pop 0.45s cubic-bezier(0.175, 0.885, 0.32, 1.275) both;
}

@keyframes ball-pop {
    0% { transform: scale(0.5) rotate(-45deg); opacity: 0; }
    100% { transform: scale(1) rotate(0deg); opacity: 1; }
}

/* Staggered animation classes dynamically set by JS */
.number.stagger-0 { animation-delay: 0.0s; }
.number.stagger-1 { animation-delay: 0.08s; }
.number.stagger-2 { animation-delay: 0.16s; }
.number.stagger-3 { animation-delay: 0.24s; }
.number.stagger-4 { animation-delay: 0.32s; }
.number.stagger-5 { animation-delay: 0.40s; }

#generate-btn {
    background: var(--button-bg);
    color: var(--button-text);
    border: none;
    padding: 1rem 2.2rem;
    font-size: 1.05rem;
    font-weight: 700;
    border-radius: 50px;
    cursor: pointer;
    box-shadow: var(--button-shadow);
    transition: all 0.3s cubic-bezier(0.165, 0.84, 0.44, 1);
    outline: none;
}

#generate-btn:hover {
    background: var(--button-hover-bg);
    transform: translateY(-3px);
    box-shadow: var(--button-hover-shadow);
}

#generate-btn:active {
    transform: translateY(-1px);
}

/* Floating Theme Toggle Button */
.theme-toggle {
    position: absolute;
    top: 2rem;
    right: 2rem;
    width: 44px;
    height: 44px;
    border-radius: 50%;
    background: var(--toggle-bg);
    border: 1px solid var(--toggle-border);
    color: var(--toggle-color);
    cursor: pointer;
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 10;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
    transition: all 0.3s cubic-bezier(0.165, 0.84, 0.44, 1);
}

.theme-toggle:hover {
    background: var(--toggle-hover-bg);
    transform: scale(1.08) rotate(15deg);
}

.theme-toggle:active {
    transform: scale(0.95);
}

.theme-toggle svg {
    width: 20px;
    height: 20px;
    transition: stroke 0.3s ease, transform 0.5s ease;
}

/* Show/hide icon depending on applied data-theme */
html[data-theme="light"] .sun-icon {
    display: none;
}
html[data-theme="light"] .moon-icon {
    display: block;
    transform: rotate(0deg);
}

html:not([data-theme="light"]) .sun-icon {
    display: block;
    transform: rotate(0deg);
}
html:not([data-theme="light"]) .moon-icon {
    display: none;
}

/* Responsive adjustment */
@media (max-width: 480px) {
    .container {
        padding: 2.5rem 1.5rem;
    }
    
    h1 {
        font-size: 2rem;
    }
    
    .number {
        width: 48px;
        height: 48px;
        font-size: 1.25rem;
    }
    
    .theme-toggle {
        top: 1.25rem;
        right: 1.25rem;
    }
}