/* Reset & Base */
*,
*::before,
*::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: var(--font-family);
    background-color: var(--color-background);
    color: var(--color-text-primary);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    /* Anti-scroll */
    height: 100vh;
    height: 100dvh;
    overflow: hidden;
    line-height: 1.2;
}

/* Layout */
.app-container {
    background-color: var(--color-surface);
    padding: var(--spacing-lg);
    border: 4px solid var(--color-border);
    /* Thick border */
    box-shadow: var(--shadow-md);
    width: 90%;
    max-width: 500px;
    text-align: center;
    /* Responsive centering */
    max-height: 90vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
}

.input-group {
    display: flex;
    flex-wrap: wrap;
    /* Fallback for very small screens */
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-lg);
    justify-content: center;
    align-items: stretch;
}

.input-group>input {
    flex: 1 1 100%;
}

.input-group>.btn {
    flex: 1 1 0px;
    min-width: 0;
}

.timer-display {
    border-top: 4px solid var(--color-border);
    border-bottom: 4px solid var(--color-border);
    padding: var(--spacing-md) 0;
    margin: var(--spacing-xl) 0;
    background-color: #ffff00;
    /* Highlight color */
}