:root {
    --bg-color: #0f172a; /* Deep modern dark blue/black */
    --surface-color: #1e293b;
    --surface-hover: #334155;
    --primary-color: #10b981; /* Neon green for workout */
    --primary-glow: rgba(16, 185, 129, 0.4);
    --secondary-color: #3b82f6; /* Cool blue for rest */
    --secondary-glow: rgba(59, 130, 246, 0.4);
    --danger-color: #ef4444; /* Red for stop/danger */
    --danger-glow: rgba(239, 68, 68, 0.4);
    --text-main: #f8fafc;
    --text-muted: #94a3b8;
    --font-family: 'Outfit', sans-serif;
}

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

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

.app-container {
    width: 100%;
    max-width: 400px; /* Mobile width optimized */
    background-color: var(--surface-color);
    border-radius: 24px;
    padding: 32px 24px;
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.4);
    display: flex;
    flex-direction: column;
    gap: 32px;
}

header {
    text-align: center;
}

h1 {
    font-size: 2rem;
    font-weight: 700;
    margin-bottom: 8px;
    letter-spacing: 1px;
}

.status-indicator {
    font-size: 1.25rem;
    font-weight: 500;
    text-transform: uppercase;
    color: var(--text-muted);
    letter-spacing: 2px;
    transition: color 0.3s ease;
}

main {
    display: flex;
    flex-direction: column;
    gap: 32px;
    align-items: center;
}

.timer-display {
    position: relative;
    width: 280px;
    height: 280px;
    display: flex;
    justify-content: center;
    align-items: center;
}

.progress-ring {
    transform: rotate(-90deg);
}

.progress-ring__path {
    transition: stroke-dashoffset 1s linear, stroke 0.3s ease;
    filter: drop-shadow(0 0 8px var(--primary-glow));
}

.time-text-container {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    text-align: center;
}

.time-text {
    font-size: 4rem;
    font-weight: 700;
    font-variant-numeric: tabular-nums; /* Monospace numbers */
}

.controls-section {
    width: 100%;
    display: flex;
    gap: 16px;
}

.input-group {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 8px;
}

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

.input-group input {
    background-color: var(--bg-color);
    border: 1px solid var(--surface-hover);
    color: var(--text-main);
    padding: 12px;
    border-radius: 12px;
    font-size: 1.25rem;
    font-weight: 500;
    text-align: center;
    font-family: var(--font-family);
    transition: border-color 0.2s;
    outline: none;
    width: 100%;
}

.input-group input:focus {
    border-color: var(--primary-color);
}

.action-buttons {
    width: 100%;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.btn {
    width: 100%;
    padding: 16px;
    border-radius: 16px;
    border: none;
    font-size: 1.125rem;
    font-weight: 700;
    font-family: var(--font-family);
    text-transform: uppercase;
    cursor: pointer;
    transition: all 0.2s ease;
    letter-spacing: 1px;
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

.start-btn {
    background-color: var(--primary-color);
    color: var(--bg-color);
    box-shadow: 0 4px 15px var(--primary-glow);
}

.start-btn:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px var(--primary-glow);
    background-color: #12cc8f;
}

.start-btn:active:not(:disabled) {
    transform: translateY(0);
}

.stop-btn {
    background-color: transparent;
    color: var(--danger-color);
    border: 2px solid var(--danger-color);
}

.stop-btn:hover:not(:disabled) {
    background-color: var(--danger-color);
    color: var(--text-main);
    box-shadow: 0 4px 15px var(--danger-glow);
}

/* Responsiveness for very small screens */
@media (max-width: 360px) {
    .app-container {
        padding: 24px 16px;
        border-radius: 0;
        height: 100vh;
        justify-content: center;
    }
    
    .timer-display {
        width: 240px;
        height: 240px;
    }
    
    .progress-ring {
        width: 240px;
        height: 240px;
    }
    
    .progress-ring__circle, .progress-ring__path {
        cx: 120;
        cy: 120;
        r: 100;
    }
    
    .time-text {
        font-size: 3.5rem;
    }
}