/* Clean, Centered UI Layout for Temperature Converter */
:root {
    --font-family: 'Plus Jakarta Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    
    --bg-gradient: linear-gradient(135deg, #0f172a 0%, #1e293b 50%, #0f172a 100%);
    --card-bg: rgba(30, 41, 59, 0.75);
    --card-border: rgba(255, 255, 255, 0.1);
    --card-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
    
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --text-muted: #64748b;
    
    --accent-blue: #38bdf8;
    --input-bg: #0f172a;
    --input-border: #334155;
    --input-focus: #38bdf8;
    
    --error-bg: rgba(239, 68, 68, 0.12);
    --error-border: rgba(239, 68, 68, 0.4);
    --error-text: #fca5a5;

    --radius-lg: 24px;
    --radius-md: 12px;
    --radius-sm: 8px;

    --transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
    font-family: var(--font-family);
    background: radial-gradient(circle at 50% 20%, #1e2e38 0%, #0d1419 60%, #06090c 100%);
    background-image: 
        radial-gradient(at 0% 0%, rgba(30, 60, 70, 0.4) 0px, transparent 50%),
        radial-gradient(at 100% 100%, rgba(15, 35, 45, 0.6) 0px, transparent 50%),
        url("https://images.unsplash.com/photo-1513002749550-c59d786b8e6c?w=1600&auto=format&fit=crop&q=80");
    background-size: cover;
    background-position: center;
    background-attachment: fixed;
    color: var(--text-primary);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 24px 16px;
    line-height: 1.5;
}

/* Centered Container */
.converter-container {
    width: 100%;
    max-width: 540px;
}

.converter-card {
    background: rgba(18, 26, 32, 0.72);
    border: 1px solid rgba(255, 255, 255, 0.15);
    backdrop-filter: blur(28px);
    -webkit-backdrop-filter: blur(28px);
    border-radius: var(--radius-lg);
    padding: 32px;
    box-shadow: 0 30px 60px -12px rgba(0, 0, 0, 0.7);
    display: flex;
    flex-direction: column;
    gap: 24px;
}

/* Card Header */
.card-header {
    text-align: center;
    display: flex;
    flex-direction: column;
    align-items: center;
}

.header-icon {
    width: 52px;
    height: 52px;
    background: rgba(56, 189, 248, 0.15);
    border: 1px solid rgba(56, 189, 248, 0.3);
    border-radius: 16px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--accent-blue);
    margin-bottom: 12px;
}

.card-header h1 {
    font-size: 1.75rem;
    font-weight: 800;
    letter-spacing: -0.025em;
    color: #ffffff;
    margin-bottom: 6px;
}

.card-header .subtitle {
    font-size: 0.9rem;
    color: var(--text-secondary);
    max-width: 420px;
}

/* Form Layout */
.form-grid {
    display: flex;
    gap: 12px;
}

@media (max-width: 480px) {
    .form-grid {
        flex-direction: column;
    }
}

.flex-input { flex: 1.4; }
.flex-unit { flex: 1; }

.form-group label {
    display: block;
    font-size: 0.8rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-secondary);
    margin-bottom: 8px;
}

.input-wrapper {
    position: relative;
    display: flex;
    align-items: center;
}

.input-wrapper input {
    width: 100%;
    height: 48px;
    background: var(--input-bg);
    border: 1.5px solid var(--input-border);
    border-radius: var(--radius-md);
    color: #ffffff;
    font-family: inherit;
    font-size: 1.05rem;
    font-weight: 600;
    padding: 0 42px 0 14px;
    outline: none;
    transition: var(--transition);
}

.input-wrapper input:focus {
    border-color: var(--input-focus);
    box-shadow: 0 0 0 3px rgba(56, 189, 248, 0.2);
}

.input-wrapper input.has-error {
    border-color: #ef4444;
    box-shadow: 0 0 0 3px rgba(239, 68, 68, 0.2);
}

.unit-symbol {
    position: absolute;
    right: 14px;
    font-weight: 700;
    font-size: 0.9rem;
    color: var(--text-muted);
}

.custom-select {
    width: 100%;
    height: 48px;
    background: var(--input-bg);
    border: 1.5px solid var(--input-border);
    border-radius: var(--radius-md);
    color: #ffffff;
    font-family: inherit;
    font-size: 0.9rem;
    font-weight: 600;
    padding: 0 32px 0 12px;
    outline: none;
    cursor: pointer;
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%2394a3b8' stroke-width='2'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 12px center;
    transition: var(--transition);
}

.custom-select:focus {
    border-color: var(--input-focus);
    box-shadow: 0 0 0 3px rgba(56, 189, 248, 0.2);
}

.custom-select option {
    background: #0f172a;
    color: #ffffff;
}

/* Validation Error Alert Box */
.error-box {
    display: flex;
    align-items: center;
    gap: 10px;
    background: var(--error-bg);
    border: 1px solid var(--error-border);
    color: var(--error-text);
    padding: 12px 16px;
    border-radius: var(--radius-md);
    font-size: 0.85rem;
    font-weight: 600;
}

.error-box.hidden {
    display: none;
}

.error-icon {
    flex-shrink: 0;
    color: #ef4444;
}

/* Button Group */
.button-group {
    display: flex;
    gap: 12px;
    margin-top: 14px;
}

.btn {
    flex: 1;
    height: 46px;
    border: none;
    border-radius: var(--radius-md);
    font-family: inherit;
    font-size: 0.95rem;
    font-weight: 700;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    transition: var(--transition);
}

.btn-primary {
    background: linear-gradient(135deg, #0284c7 0%, #0369a1 100%);
    color: #ffffff;
    box-shadow: 0 4px 12px rgba(2, 132, 199, 0.3);
}

.btn-primary:hover {
    background: linear-gradient(135deg, #0369a1 0%, #075985 100%);
    transform: translateY(-1px);
}

.btn-secondary {
    background: #1e293b;
    color: var(--text-secondary);
    border: 1px solid var(--input-border);
}

.btn-secondary:hover {
    background: #334155;
    color: #ffffff;
}

/* Presets Section */
.presets-section {
    display: flex;
    flex-direction: column;
    gap: 8px;
    border-top: 1px solid rgba(255, 255, 255, 0.08);
    padding-top: 18px;
}

.presets-label {
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.04em;
}

.preset-chips {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

.chip {
    background: rgba(15, 23, 42, 0.6);
    border: 1px solid var(--input-border);
    color: var(--text-secondary);
    padding: 6px 12px;
    border-radius: 20px;
    font-size: 0.775rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
}

.chip:hover {
    border-color: var(--accent-blue);
    color: var(--accent-blue);
    background: rgba(56, 189, 248, 0.08);
}

/* Results Section */
.results-section {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.results-section h2 {
    font-size: 0.95rem;
    font-weight: 700;
    color: var(--text-secondary);
}

.results-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 12px;
}

@media (max-width: 520px) {
    .results-grid {
        grid-template-columns: 1fr;
    }
}

.result-card {
    background: #0f172a;
    border: 1.5px solid var(--input-border);
    border-radius: var(--radius-md);
    padding: 14px;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    gap: 10px;
    transition: var(--transition);
}

.result-card.source-active {
    border-color: var(--accent-blue);
    background: linear-gradient(180deg, rgba(56, 189, 248, 0.08) 0%, rgba(15, 23, 42, 1) 100%);
}

.card-header-inner {
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.unit-name {
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-secondary);
}

.badge {
    background: #1e293b;
    color: var(--accent-blue);
    font-size: 0.725rem;
    font-weight: 800;
    padding: 2px 7px;
    border-radius: 6px;
    border: 1px solid rgba(56, 189, 248, 0.2);
}

.value-display {
    font-size: 1.35rem;
    font-weight: 800;
    color: #ffffff;
    word-break: break-all;
    line-height: 1.2;
}

.copy-btn {
    background: transparent;
    border: 1px solid var(--input-border);
    color: var(--text-muted);
    border-radius: var(--radius-sm);
    padding: 5px 8px;
    font-size: 0.725rem;
    font-weight: 600;
    cursor: pointer;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 5px;
    transition: var(--transition);
}

.copy-btn:hover {
    color: var(--text-primary);
    border-color: var(--text-secondary);
    background: #1e293b;
}

.copy-btn.copied {
    border-color: #22c55e;
    color: #22c55e;
    background: rgba(34, 197, 94, 0.1);
}