:root {
    --color-primary:        #1a73e8;
    --color-primary-tint:   #e8f0fe;
    --color-primary-border: #b3c8f5;
    --color-primary-dark:   #1558b0;
    --color-error:          #d93025;
    --color-error-tint:     #fce8e6;
    --color-success:        #188038;
    --color-success-tint:   #e6f4ea;
    --color-success-border: #a8d5b0;
    --color-text:           #222;
    --color-muted:          #555;
    --color-subtle:         #888;
    --color-disabled:       #bbb;
    --color-border:         #ddd;
    --color-border-in:      #ccc;
    --color-border-subtle:  #eee;
    --color-bg:             #f4f4f4;
    --color-bg-card:        #fff;
    --color-bg-input:       #fafafa;
    --color-bg-subtle:      #f0f0f0;
    --radius:               4px;
    --transition:           0.15s;
}

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

body {
    text-align: center;
    font-family: sans-serif;
    background: var(--color-bg);
    color: var(--color-text);
    padding: clamp(0.5rem, 2vw, 1rem);
}

h1 {
    margin-bottom: 2rem;
}

h2 {
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--color-muted);
    margin-bottom: 1rem;
    margin-top: 1rem;
    border-bottom: 1px solid var(--color-border);
    padding-bottom: 0.4rem;
}

.section {
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: 6px;
    padding: 1.5rem;
    margin: 0 auto 0.75rem;
    max-width: calc(1000px + 3rem);
}

.section--narrow {
    max-width: calc(500px + 3rem);
}

.section--wide {
    max-width: calc(1500px + 3rem);
}

/* --- Subtitle --- */
.subtitle {
    color: var(--color-subtle);
    font-size: 1rem;
    margin: -1.5rem 0 2rem;
}

/* --- Labels & Inputs --- */
.field {
    display: flex;
    flex-direction: column;
    gap: 0.3rem;
    margin-bottom: 1rem;
}

label {
    font-size: 0.875rem;
    font-weight: 600;
}

.unit {
    font-size: 0.75rem;
    color: var(--color-subtle);
    font-weight: normal;
}

:is(input[type="number"], input[type="text"], select, textarea) {
    width: 100%;
    padding: 0.5rem 0.75rem;
    border: 1px solid var(--color-border-in);
    border-radius: var(--radius);
    font-size: 0.95rem;
    background: var(--color-bg-input);
    transition: border-color var(--transition);
}

:is(input[type="number"], input[type="text"], select, textarea):focus {
    outline: none;
    border-color: var(--color-primary);
    background: var(--color-bg-card);
}

:is(input[type="number"], input[type="text"]).error {
    border-color: var(--color-error);
}

.hint {
    font-size: 0.75rem;
    color: var(--color-subtle);
}

.error-msg {
    font-size: 0.75rem;
    color: var(--color-error);
}

/* --- Input with inline unit --- */
.input-unit {
    display: flex;
    align-items: center;
    border: 1px solid var(--color-border-in);
    border-radius: var(--radius);
    overflow: hidden;
    background: var(--color-bg-input);
}

.input-unit input {
    border: none;
    background: transparent;
    flex: 1;
    padding: 0.5rem 0.75rem;
}

.input-unit input:focus {
    outline: none;
}

.input-unit .unit-badge {
    padding: 0 0.75rem;
    background: var(--color-border-subtle);
    color: var(--color-muted);
    font-size: 0.85rem;
    border-left: 1px solid var(--color-border-in);
    white-space: nowrap;
    align-self: stretch;
    display: flex;
    align-items: center;
}

/* --- Buttons --- */
.btn-row {
    display: flex;
    gap: 0.75rem;
    flex-wrap: wrap;
    margin-top: 0.5rem;
}

button {
    padding: 0.5rem 1.25rem;
    font-size: 0.95rem;
    border-radius: var(--radius);
    cursor: pointer;
    border: 1px solid transparent;
    transition: background var(--transition), border-color var(--transition);
}

.btn-primary {
    background: var(--color-primary);
    color: var(--color-bg-card);
    border-color: var(--color-primary);
}

.btn-primary:hover { background: var(--color-primary-dark); }

.btn-secondary {
    background: var(--color-bg-card);
    color: var(--color-primary);
    border-color: var(--color-primary);
}

.btn-secondary:hover { background: var(--color-primary-tint); }

.btn-danger {
    background: var(--color-bg-card);
    color: var(--color-error);
    border-color: var(--color-error);
}

.btn-danger:hover { background: var(--color-error-tint); }

button:disabled {
    opacity: 0.45;
    cursor: not-allowed;
}

/* --- Shape selector --- */
.shape-select {
    margin-bottom: 1rem;
}

/* --- Calculator layout --- */
.two-columns,
.three-columns {
    display: grid;
    gap: 1rem;
    align-items: start;
}

.one-column    { grid-template-columns: 1fr; }
.two-columns   { grid-template-columns: repeat(auto-fit, minmax(min(360px, 100%), 1fr)); }
.three-columns { grid-template-columns: repeat(auto-fit, minmax(min(280px, 100%), 1fr)); }

.inputs,
.formulas,
.results {
    min-width: 0;
    display: flex;
    flex-direction: column;
}

.inputs > h2:first-child,
.formulas > h2:first-child,
.results > h2:first-child {
    margin-top: 0;
}

.results {
    gap: 0.5rem;
}

/* --- Formulas panel --- */
.formulas {
    font-size: 0.85rem;
    color: var(--color-muted);
}

/* --- Shape form visibility --- */
.shape-form { display: none; }
.shape-form.active { display: block; }

/* --- Shape icon --- */
.shape-icon {
    display: flex;
    justify-content: center;
    margin-bottom: 1.25rem;
}

/* --- Result box --- */
.result-box {
    background: var(--color-primary-tint);
    border: 1px solid var(--color-primary-border);
    border-radius: var(--radius);
    padding: 1rem 1.25rem;
    text-align: center;
}

.result-box.success {
    background: var(--color-success-tint);
    border-color: var(--color-success-border);
}

.result-box.success .result-value { color: var(--color-success); }

.result-box.empty .result-value { color: var(--color-disabled); }

.result-box .result-label {
    font-size: 0.8rem;
    color: var(--color-muted);
    margin-bottom: 0.25rem;
}

.result-box .result-value {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--color-primary);
}

.result-box .result-unit {
    font-size: 0.9rem;
    color: var(--color-muted);
    margin-left: 0.25rem;
}

/* --- Radio & Checkbox --- */
.radio-group,
.checkbox-group {
    display: flex;
    flex-direction: column;
    gap: 0.4rem;
}

.radio-group label,
.checkbox-group label {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-weight: normal;
    cursor: pointer;
}

/* --- Table --- */
table {
    width: auto;
    max-width: 100%;
    border-collapse: collapse;
    font-size: 0.9rem;
}

th {
    background: var(--color-bg-subtle);
    padding: 0.4rem 0.4rem;
    border-bottom: 2px solid var(--color-border);
    word-break: break-word;
}

td {
    padding: 0.4rem 0.4rem;
    border-bottom: 1px solid var(--color-border-subtle);
}