/* ---------------------------------------------------
   Tokens
--------------------------------------------------- */
:root {
    --paper:      #F7F4EC;
    --paper-line: #DDD6C4;
    --ink:        #211F1B;
    --ink-muted:  #6E6658;
    --navy:       #23395D;
    --navy-hover: #33507F;
    --correct:    #2F6B4A;
    --wrong:      #AE3A2A;

    --font-head: 'IBM Plex Serif', Georgia, serif;
    --font-body: 'IBM Plex Sans', system-ui, sans-serif;
    --font-mono: 'IBM Plex Mono', ui-monospace, monospace;
}

/* ---------------------------------------------------
   Base
--------------------------------------------------- */
* {
    box-sizing: border-box;
}

body {
    margin: 0;
    padding: 48px 20px 80px;
    background: var(--paper);
    color: var(--ink);
    font-family: var(--font-body);
    font-size: 16px;
    line-height: 1.5;
}

#app {
    max-width: 600px;
    margin: 0 auto;
    border: 1px solid var(--paper-line);
    background: #FFFDF8;
    padding: 40px 44px;
}

@media (max-width: 640px) {
    #app {
        padding: 28px 22px;
    }
}

section h1 {
    font-family: var(--font-head);
    font-weight: 600;
    font-size: 1.5rem;
    margin: 0 0 20px;
    padding-bottom: 14px;
    border-bottom: 1px solid var(--paper-line);
}

section h2 {
    font-family: var(--font-head);
    font-weight: 400;
    font-size: 1.05rem;
    margin: 32px 0 14px;
    color: var(--ink);
}

.hidden {
    display: none;
}

/* ---------------------------------------------------
   Buttons (rectangular, ink outline — no rounded SaaS look)
--------------------------------------------------- */
button {
    font-family: var(--font-body);
    font-size: 0.95rem;
    font-weight: 500;
    color: var(--ink);
    background: transparent;
    border: 1px solid var(--ink);
    border-radius: 0;
    padding: 9px 16px;
    cursor: pointer;
    transition: background-color 0.15s ease, color 0.15s ease, border-color 0.15s ease;
}

button:hover {
    background: var(--navy);
    border-color: var(--navy);
    color: var(--paper);
}

button:focus-visible {
    outline: 2px solid var(--navy);
    outline-offset: 2px;
}

#constant-buttons,
#choice-buttons,
#other-modes-buttons {
    display: flex;
    gap: 10px;
    flex-wrap: wrap;
}

.constant-btn.active {
    background: var(--navy);
    border-color: var(--navy);
    color: var(--paper);
}

/* ---------------------------------------------------
   Free mode
--------------------------------------------------- */
.free-mode {
    margin-top: 24px;
    padding-top: 20px;
    border-top: 1px dashed var(--paper-line);
    display: flex;
    align-items: center;
    gap: 10px;
    flex-wrap: wrap;
}

.free-mode label {
    color: var(--ink-muted);
    font-size: 0.92rem;
}

.free-mode input[type="number"] {
    width: 90px;
}

/* ---------------------------------------------------
   Inputs — underline style, numeric fields in mono
--------------------------------------------------- */
input[type="text"],
input[type="number"] {
    font-family: var(--font-mono);
    font-size: 1.05rem;
    color: var(--ink);
    background: transparent;
    border: none;
    border-bottom: 1px solid var(--ink);
    border-radius: 0;
    padding: 7px 2px;
}

input[type="text"]:focus,
input[type="number"]:focus {
    outline: none;
    border-bottom: 2px solid var(--navy);
}

#pi-input {
    width: 100%;
    margin-top: 8px;
}

#input-actions {
    margin-top: 20px;
    display: flex;
    gap: 10px;
}

.hint {
    color: var(--ink-muted);
    font-size: 0.92rem;
    margin: 0 0 4px;
}

#constant-label-input,
#integer-part-input {
    font-family: var(--font-mono);
}

/* ---------------------------------------------------
   Errors
--------------------------------------------------- */
.error {
    color: var(--wrong);
    font-size: 0.88rem;
    margin: 8px 0 0;
}

/* ---------------------------------------------------
   Result — graded like a checked exam
--------------------------------------------------- */
.result-block {
    margin-bottom: 18px;
}

.result-label {
    color: var(--ink-muted);
    font-size: 0.88rem;
    margin: 0 0 4px;
}

.pi-value {
    font-family: var(--font-mono);
    font-size: 1.2rem;
    letter-spacing: 0.02em;
    word-break: break-all;
    line-height: 1.7;
    margin: 0;
}

.digit-ok {
    color: var(--ink);
}

.digit-wrong {
    color: var(--wrong);
    text-decoration: underline;
    text-decoration-style: wavy;
    text-decoration-thickness: 1px;
}

#result-score {
    font-size: 1rem;
    color: var(--ink-muted);
    margin: 0 0 28px;
}

#other-modes {
    margin: 0 0 28px;
    padding-top: 24px;
    border-top: 1px solid var(--paper-line);
}

#other-modes > .result-label {
    margin-bottom: 12px;
}

#other-constant-buttons {
    margin-top: 10px;
}

#retry-btn {
    color: var(--ink-muted);
    border-color: var(--paper-line);
}

#retry-btn:hover {
    background: var(--ink);
    border-color: var(--ink);
    color: var(--paper);
}

/* ---------------------------------------------------
   Reduced motion
--------------------------------------------------- */
@media (prefers-reduced-motion: reduce) {
    button {
        transition: none;
    }
}