:root {
    --bg-color: #121826;
    --container-bg: #1f2937;
    --primary-accent: #2dd4bf;
    --secondary-accent: #67e8f9;
    --text-color: #e5e7eb;
    --text-subtle: #9ca3af;
    --input-bg: #374151;
    --border-color: #4b5563;
    --error-color: #f87171;

    --font-family: 'Poppins', sans-serif;
}

body {
    font-family: var(--font-family);
    background: var(--bg-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    padding: 20px;
    box-sizing: border-box;
}

.container {
    max-width: 900px;
    width: 100%;
    background: var(--container-bg);
    padding: 30px 40px;
    border-radius: 15px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.4);
    display: flex;
    flex-direction: column;
    align-items: center;
    border: 1px solid var(--border-color);
    transition: border-color 0.4s, box-shadow 0.4s;
}

h1 {
    color: var(--primary-accent);
    font-weight: 600;
    margin-bottom: 10px;
    transition: color 0.4s;
}

p {
    color: var(--text-subtle);
    margin-bottom: 25px;
    text-align: center;
}

#collatzForm {
    display: flex;
    align-items: center;
    gap: 15px;
    margin-bottom: 20px;
    position: relative;
}

input[type="number"] {
    padding: 12px 15px;
    font-size: 16px;
    font-family: var(--font-family);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    background-color: var(--input-bg);
    color: var(--text-color);
    width: 180px;
    transition: border-color 0.3s, box-shadow 0.3s, opacity 0.4s;
}

input[type="number"]:focus {
    outline: none;
    border-color: var(--primary-accent);
    box-shadow: 0 0 0 3px rgba(45, 212, 191, 0.3);
}

input[type=number]::-webkit-inner-spin-button,
input[type=number]::-webkit-outer-spin-button {
  -webkit-appearance: none;
  margin: 0;
}
input[type=number] {
  -moz-appearance: textfield;
}

button {
    padding: 12px 25px;
    font-size: 16px;
    font-family: var(--font-family);
    font-weight: 600;
    background: var(--primary-accent);
    color: var(--bg-color);
    border: none;
    border-radius: 8px;
    cursor: pointer;
    transition: background 0.3s, transform 0.2s, box-shadow 0.3s, opacity 0.4s;
    box-shadow: 0 4px 10px rgba(45, 212, 191, 0.2);
}

button:hover {
    background: var(--secondary-accent);
    transform: translateY(-2px);
    box-shadow: 0 6px 15px rgba(103, 232, 249, 0.3);
}

button:active {
    transform: translateY(0);
    box-shadow: 0 2px 5px rgba(45, 212, 191, 0.2);
}

.crazy-mode-controls {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 20px;
    color: var(--text-subtle);
}

.switch {
    position: relative;
    display: inline-block;
    width: 50px;
    height: 26px;
}

.switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: var(--input-bg);
    transition: .4s;
    border: 1px solid var(--border-color);
}

.slider:before {
    position: absolute;
    content: "";
    height: 18px;
    width: 18px;
    left: 3px;
    bottom: 3px;
    background-color: var(--text-subtle);
    transition: .4s;
}

input:checked + .slider {
    background-color: var(--secondary-accent);
    border-color: var(--secondary-accent);
}

input:focus + .slider {
    box-shadow: 0 0 1px var(--secondary-accent);
}

input:checked + .slider:before {
    transform: translateX(24px);
    background-color: var(--bg-color);
}

.slider.round {
    border-radius: 26px;
}
.slider.round:before {
    border-radius: 50%;
}

.container.crazy-active {
    border-color: var(--secondary-accent);
    box-shadow: 0 10px 30px rgba(103, 232, 249, 0.3);
}

.container.crazy-active h1 {
    color: var(--secondary-accent);
}

.container.crazy-active .stats-display strong {
    color: var(--secondary-accent);
}

.container.crazy-active #calculateButton,
.container.crazy-active #numberInput {
    opacity: 0.5;
    pointer-events: none;
}

.loader {
    display: none;
    width: 20px;
    height: 20px;
    border: 3px solid var(--text-subtle);
    border-top-color: var(--primary-accent);
    border-radius: 50%;
    animation: spin 1s linear infinite;
    margin-left: 10px;
}

@keyframes spin {
    to {
        transform: rotate(360deg);
    }
}

.loader.visible {
    display: inline-block;
}

.svg-container {
    width: 100%;
    max-width: 100%;
    aspect-ratio: 16 / 9;
    margin-top: 20px;
    background: var(--input-bg);
    border-radius: 10px;
    position: relative;
    overflow: hidden;
    border: 1px solid var(--border-color);
}

#visualization {
    display: block;
    width: 100%;
    height: 100%;
}

.number-display {
    font-size: 18px;
    margin-top: 20px;
    color: var(--secondary-accent);
    min-height: 1.3em;
    text-align: center;
    font-weight: 600;
    letter-spacing: 0.5px;
}

.stats-display {
    font-size: 15px;
    margin-top: 25px;
    color: var(--text-subtle);
    background: var(--input-bg);
    padding: 20px;
    border-radius: 10px;
    line-height: 1.7;
    width: calc(100% - 40px);
    text-align: left;
    border: 1px solid var(--border-color);
    transition: border-color 0.4s;
}

.stats-display strong {
    color: var(--text-color);
    font-weight: 600;
    transition: color 0.4s;
}

.stats-display span {
    color: var(--primary-accent);
    font-weight: 600;
    margin-left: 5px;
}

.path {
    fill: none;
    stroke: var(--primary-accent);
    stroke-width: 2.5;
    stroke-linecap: round;
    stroke-linejoin: round;
    transition: stroke-dashoffset var(--animation-duration, 1.5s) cubic-bezier(0.65, 0, 0.35, 1);
    filter: drop-shadow(0 0 3px rgba(45, 212, 191, 0.7));
}

.path.drawing {
    stroke-dasharray: var(--path-length);
    stroke-dashoffset: var(--path-length);
}

.point {
    fill: var(--text-color);
    stroke: var(--bg-color);
    stroke-width: 1;
    transition: r 0.2s ease-in-out, fill 0.2s ease-in-out, filter 0.2s ease-in-out, opacity 0.3s ease;
    cursor: pointer;
}

.point:hover {
    fill: var(--secondary-accent);
    filter: drop-shadow(0 0 5px rgba(103, 232, 249, 0.8));
}