:root {
    /* Color Palette (Material Inspired Dark Theme) */
    --color-primary: #8BC34A; /* Light Green for active/in-breath */
    --color-secondary: #FF5252; /* Red/Amber for out-breath */
    --color-background: #121212; /* Dark background */
    --color-surface: #1E1E1E; /* Elevated surface color */
    --color-text-primary: #E0E0E0; /* Light text */
    --color-text-secondary: #A0A0A0; /* Muted text */
    
    /* Layout Constants (unchanged) */
    --spacing-unit: 16px;
    --border-radius-large: 12px;
}


body.light-mode {
    --color-primary: #4CAF50; /* A darker green for visibility on light BG */
    --color-secondary: #F44336; /* Classic Red */
    --color-background: #FAFAFA; /* Lightest Gray */
    --color-surface: #FFFFFF; /* White */
    --color-text-primary: #212121; /* Dark Gray text */
    --color-text-secondary: #757575; /* Muted Dark Gray text */
}

/* Global Styles & Body (UNCHANGED) */
body {
    font-family: 'Roboto', sans-serif;
    /* Uses CSS variables which will be updated by the class */
    background-color: var(--color-background); 
    color: var(--color-text-primary);
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    transition: background-color 0.3s;
}

.mode-toggle {
    position: fixed; /* Fixed position */
    top:  calc(2 * var(--spacing-unit));
    left:  calc(2 * var(--spacing-unit));
    z-index: 1000;
    padding:  calc(2 * var(--spacing-unit));
    background-color: var(--color-surface); /* Uses surface color */
    border-radius: var(--border-radius-large);
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

.mode-toggle:hover {
    /* Slightly different hover effect for better visibility */
    background-color: var(--color-text-secondary); 
}

.secondary-button {
    background-color: #333; /* Dark mode background */
    color: var(--color-text-primary);
}

body.light-mode .secondary-button {
    background-color: #E0E0E0; /* Light mode background */
    color: var(--color-text-primary);
}

/* --- Layout Container --- */
.timer-container {
    display: flex;
    flex-direction: column;
    width: 100%;
    max-width: 600px; /* Max width for large screens */
    height: 100vh; /* Full height on mobile */
    box-sizing: border-box;
    padding: calc(2 * var(--spacing-unit));
}

/* --- Breathing Indicator (Ball) --- */
.breathing-display-area {
    flex-grow: 1; /* Takes up all available space */
    display: flex;
    justify-content: center;
    align-items: center;
    margin-bottom:  calc(2 * var(--spacing-unit));
}

.breathing-ball {
    width: 200px;
    height: 200px;
    border-radius: 50%;
    background-color: var(--color-surface);
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.4);
    transition: 
        transform 0.5s ease-in-out, 
        background-color 0.5s ease, 
        box-shadow 0.5s ease; 
    will-change: transform; 
}

/* Breathing States */
.breathing-ball.resting {
    background-color: var(--color-surface);
    transform: scale(1);
    box-shadow: 0 6px 12px rgba(0, 0, 0, 0.5);
}

.breathing-ball.expanding {
    background-color: var(--color-secondary);
    transform: scale(1.6); /* In-breath: ball expands */
    box-shadow: 0 0 30px var(--color-secondary);
}

.breathing-ball.contracting {
    background-color: var(--color-primary);
    transform: scale(1); /* Out-breath: ball contracts */
    box-shadow: 0 0 10px var(--color-primary);
}

/* --- Controls Container --- */
.controls-container {
    background-color: var(--color-surface);
    padding: calc(2 * var(--spacing-unit));
    border-radius: var(--border-radius-large);
    box-shadow: 0 8px 16px rgba(0, 0, 0, 0.5);
    display: flex;
    flex-direction: column;
    gap: calc(2 * var(--spacing-unit));
}

/* Timer Display */
.timer-display {
    font-size: 3em;
    font-weight: 300;
    text-align: center;
    letter-spacing: 2px;
}

/* --- Breathing Rate Control --- */
.breathing-rate-control {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: var(--spacing-unit);
    padding: var(--spacing-unit) 0;
    border-top: 1px solid #333;
    border-bottom: 1px solid #333;
}

.rate-indicator-container {
    display: flex;
    gap: 8px;
    padding: 0 calc(2 * var(--spacing-unit));
}

.rate-indicator {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background-color: var(--color-text-secondary);
    transition: background-color 0.3s;
}

.rate-indicator.active {
    background-color: var(--color-primary);
}

/* --- Buttons --- */
.main-buttons {
    display: flex;
    justify-content: space-around;
    gap: var(--spacing-unit);
}

.icon-button {
    background: none;
    border: none;
    color: var(--color-text-primary);
    cursor: pointer;
    padding: var(--spacing-unit);
    transition: background-color 0.2s;
    border-radius: 50%;
}

.icon-button:hover:not(:disabled) {
    background-color: rgba(255, 255, 255, 0.1);
}

.main-button {
    flex: 1;
    padding: var(--spacing-unit);
    border: none;
    border-radius: var(--border-radius-large);
    font-size: 1.2em;
    font-weight: 500;
    cursor: pointer;
    transition: background-color 0.2s, box-shadow 0.2s;
    display: flex;
    justify-content: center;
    align-items: center;
}

.primary-button {
    background-color: var(--color-primary);
    color: var(--color-surface);
    box-shadow: 0 4px 8px rgba(139, 195, 74, 0.4);
}

.primary-button:hover:not(:disabled) {
    background-color: #A5D6A7; /* Lighter shade on hover */
    box-shadow: 0 6px 12px rgba(139, 195, 74, 0.6);
}

.secondary-button {
    background-color: #333;
    color: var(--color-text-primary);
}

.secondary-button:hover:not(:disabled) {
    background-color: #444;
}

.pause-state-button {
    background-color: #FFC107; /* Amber/Yellow for 'Pause' warning */
    color: var(--color-surface);
    box-shadow: 0 4px 8px rgba(255, 193, 7, 0.4);
}

.pause-state-button:hover:not(:disabled) {
    background-color: #FFD54F; /* Lighter shade on hover */
    box-shadow: 0 6px 12px rgba(255, 193, 7, 0.6);
}

.main-button:disabled, .icon-button:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    box-shadow: none;
}

/* Adjustments for Material Symbols (icons) */
.material-symbols-outlined {
  font-size: 3em;
  font-variation-settings:
  'FILL' 0,
  'wght' 400,
  'GRAD' 0,
  'opsz' 48;
}

@media (max-width: 400px) {
    .rate-indicator-container {
        padding: 0 var(--spacing-unit);
    }
}

@media (max-width: 300px) {
    .rate-indicator-container {
        padding: 0 0;
    }
}


@media (max-height: 680px) {
    .breathing-ball {
        width: 160px;
        height: 160px;
    }

    .controls-container {
        padding: calc(1.5 * var(--spacing-unit));
        gap: calc(1.5 * var(--spacing-unit));
    }

    .timer-display {
        font-size: 2.2em;
    }

    .icon-button {
        padding: 8px;
    }
}

@media (max-width: 400px) {
    .rate-indicator-container {
        padding: 0 var(--spacing-unit);
    }
}

@media (max-height: 500px) {
    .mode-toggle {
        top:  var(--spacing-unit);
        left:  var(--spacing-unit);
    }

    .breathing-ball {
        width: 120px;
        height: 120px;
    }

    .timer-container {
        padding: var(--spacing-unit);
    }

    .controls-container {
        padding: var(--spacing-unit);
        gap: var(--spacing-unit);
    }

    .timer-display {
        font-size: 1.8em;
    }

    .main-button {
        padding: 10px;
        font-size: 1em;
    }

    .icon-button {
        padding: 6px;
    }

    .breathing-rate-control {
        padding: 4px 0;
    }
}

@media (max-height: 380px) {
    .mode-toggle {
        top: var(--spacing-unit);
        left: var(--spacing-unit);
    }

    .breathing-ball {
        width: 90px;
        height: 90px;
    }

    .timer-display {
        font-size: 1.4em;
        margin-bottom: 0px;
    }

    .controls-container {
        padding: 8px;
        gap: 8px;
    }

    .main-buttons {
        gap: 6px;
    }

    .main-button {
        padding: 6px;
        font-size: 0.9em;
    }

    .breathing-rate-control {
        gap: 6px;
    }

    .rate-indicator {
        width: 6px;
        height: 6px;
    }
}