:root {
    --bg-dark: #0f172a;
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --accent-color: #38bdf8;
    --accent-glow: rgba(56, 189, 248, 0.4);
    --card-bg: rgba(30, 41, 59, 0.7);
    --card-border: rgba(255, 255, 255, 0.1);
    --input-bg: rgba(15, 23, 42, 0.5);
    --font-main: 'Outfit', sans-serif;
    --transition-speed: 0.3s;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: var(--font-main);
    background-color: var(--bg-dark);
    color: var(--text-primary);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    overflow-x: hidden;
}

.background-glow {
    position: fixed;
    top: -20%;
    left: -20%;
    width: 140%;
    height: 140%;
    background: radial-gradient(circle at 50% 50%, var(--accent-glow) 0%, transparent 60%);
    opacity: 0.15;
    z-index: -1;
    pointer-events: none;
}

.container {
    width: 100%;
    max-width: 480px;
    padding: 2rem;
    display: flex;
    flex-direction: column;
    gap: 2rem;
}

.navbar {
    display: flex;
    justify-content: center;
    gap: 2rem;
    margin-bottom: 2rem;
    padding: 1rem;
    background: var(--card-bg);
    backdrop-filter: blur(12px);
    border-radius: 16px;
    border: 1px solid var(--card-border);
}

.nav-link {
    color: var(--text-secondary);
    text-decoration: none;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    font-size: 0.875rem;
    transition: color var(--transition-speed);
}

.nav-link:hover,
.nav-link.active {
    color: var(--accent-color);
    text-shadow: 0 0 10px var(--accent-glow);
}

header {
    text-align: center;
}

header h1 {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
    letter-spacing: -0.05em;
    background: linear-gradient(135deg, #fff 0%, var(--accent-color) 100%);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

header p {
    color: var(--text-secondary);
    font-weight: 300;
}

.converter-card {
    background: var(--card-bg);
    backdrop-filter: blur(12px);
    border: 1px solid var(--card-border);
    border-radius: 24px;
    padding: 2rem;
    box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.converter-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 30px 60px -12px rgba(0, 0, 0, 0.6);
}

.tabs {
    display: flex;
    background: var(--input-bg);
    border-radius: 12px;
    padding: 0.25rem;
    gap: 0.25rem;
}

.tab {
    flex: 1;
    background: transparent;
    border: none;
    color: var(--text-secondary);
    padding: 0.75rem;
    border-radius: 10px;
    font-family: inherit;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-speed);
}

.tab:hover {
    color: var(--text-primary);
}

.tab.active {
    background: var(--accent-color);
    color: var(--bg-dark);
    box-shadow: 0 4px 12px var(--accent-glow);
}

.input-group {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
    transition: opacity 0.3s ease, transform 0.3s ease;
}

.input-group.hidden {
    display: none;
}

.input-group label {
    font-size: 0.875rem;
    color: var(--text-secondary);
    font-weight: 500;
}

.label-row {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 0.25rem;
}

.unit-select {
    background: transparent;
    color: var(--accent-color);
    border: none;
    font-family: inherit;
    font-size: 0.875rem;
    font-weight: 700;
    cursor: pointer;
    outline: none;
    text-align: right;
    padding-left: 0.5rem;
}

.unit-select option {
    background: var(--bg-dark);
    color: var(--text-primary);
}

.unit-display-row {
    display: flex;
    justify-content: center;
    margin-top: 0.5rem;
}

.result-unit-select {
    font-size: 1rem;
    color: var(--text-secondary);
    font-weight: 500;
    text-align: center;
}

input[type="number"] {
    width: 100%;
    background: var(--input-bg);
    border: 2px solid var(--card-border);
    border-radius: 12px;
    padding: 1rem;
    font-family: inherit;
    font-size: 1.25rem;
    color: var(--text-primary);
    outline: none;
    transition: all var(--transition-speed);
}

input[type="number"]:focus {
    border-color: var(--accent-color);
    box-shadow: 0 0 0 4px rgba(56, 189, 248, 0.1);
}

.result-display {
    background: rgba(0, 0, 0, 0.3);
    border-radius: 16px;
    padding: 1.5rem;
    text-align: center;
    margin-top: 1rem;
    border: 1px solid var(--card-border);
}

.result-display .label {
    display: block;
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
}

.result-display .value {
    font-size: 3rem;
    font-weight: 700;
    color: var(--accent-color);
    line-height: 1;
    margin-bottom: 0.5rem;
}

.result-display .unit {
    font-size: 1rem;
    color: var(--text-secondary);
}

/* Chrome, Safari, Edge, Opera */
input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button {
    -webkit-appearance: none;
    appearance: none;
    margin: 0;
}

/* Firefox */
input[type=number] {
    -moz-appearance: textfield;
}

@media (max-width: 480px) {
    .container {
        padding: 1rem;
    }

    header h1 {
        font-size: 2rem;
    }

    .result-display .value {
        font-size: 2.5rem;
    }
}