:root {
    /* Dark theme palette (default) */
    --bg-1: #0d0d0d;
    /* deep black */
    --bg-2: #1a1a1a;
    /* charcoal */
    --card-bg: rgba(255, 255, 255, 0.03);
    --accent: #ff6f61;
    /* coral red */
    --accent-2: #ffb347;
    /* warm orange */
    --muted: #b0b0b0;
    --text: #f5f5f5;
    --glass-border: rgba(255, 255, 255, 0.06);
    --panel-radius: 12px;
    --select-bg: #1a1a1a;
    --select-text: #f5f5f5;
}

/* Light theme overrides */
body.light {
    --bg-1: #ffffff;
    --bg-2: #f2f2f2;
    --card-bg: linear-gradient(180deg, rgba(255, 255, 255, 0.9), rgba(245, 245, 245, 0.8));
    --accent: #ff6f61;
    /* coral red */
    --accent-2: #ffb347;
    /* warm orange */
    --muted: #555555;
    --text: #1a1a1a;
    --glass-border: rgba(0, 0, 0, 0.08);
    --select-bg: #f2f2f2;
    --select-text: #1a1a1a;
}

/* Base resets */
* {
    box-sizing: border-box;
    font-family: Inter, system-ui, Segoe UI, Roboto, Arial;
}

html,
body {
    height: 100%;
    margin: 0;
}

body {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    color: var(--text);
    background: radial-gradient(circle at 10% 10%, var(--bg-1) 0%, var(--bg-2) 100%);
    -webkit-font-smoothing: antialiased;
}

/* header */
.topbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 12px 18px;
    border-bottom: 1px solid var(--glass-border);
    backdrop-filter: blur(6px);
}

.brand {
    font-weight: 700;
    font-size: 16px;
}

.actions .btn {
    font-size: 13px;
}

/* layout */
.container {
    max-width: 1100px;
    margin: 28px auto;
    width: calc(100% - 40px);
    display: grid;
    grid-template-columns: 1fr 340px;
    gap: 20px;
    align-items: start;
    flex: 1 0 auto;
    padding-bottom: 20px;
}

/* panels */
.panel {
    background: var(--card-bg);
    padding: 18px;
    border-radius: var(--panel-radius);
    border: 1px solid var(--glass-border);
    box-shadow: 0 14px 30px rgba(0, 0, 0, 0.4);
}

.panel.small {
    padding: 14px;
}

/* rows & inputs */
.row {
    display: flex;
    flex-direction: column;
    margin-bottom: 10px;
}

.row.double {
    display: grid;
    grid-template-columns: 1fr 160px 160px;
    gap: 10px;
    align-items: end;
}

.inline-row {
    display: flex;
    gap: 8px;
    align-items: center;
}

label {
    font-size: 13px;
    color: var(--muted);
    margin-bottom: 6px;
}

input[type="number"],
select {
    padding: 10px 12px;
    border-radius: 10px;
    border: 1px solid var(--glass-border);
    background: transparent;
    color: var(--text);
    outline: none;
    font-size: 15px;
    appearance: none;
}

/* dropdown */
select {
    background-color: var(--select-bg) !important;
    color: var(--select-text) !important;
    border: 1px solid var(--glass-border);
    padding-right: 30px;
}

select:focus {
    box-shadow: 0 6px 18px rgba(0, 0, 0, 0.25);
}

/* button styles */
.controls {
    display: flex;
    gap: 10px;
    align-items: center;
    flex-wrap: wrap;
}

.btn {
    padding: 9px 12px;
    border-radius: 10px;
    border: 1px solid var(--glass-border);
    background: transparent;
    color: var(--text);
    cursor: pointer;
    font-weight: 600;
    transition: background 0.3s ease, transform 0.2s ease;
}

.btn:hover {
    transform: translateY(-2px);
}

.btn.primary {
    background: linear-gradient(90deg, var(--accent), var(--accent-2));
    color: #fff;
    border: none;
    box-shadow: 0 8px 18px rgba(255, 111, 97, 0.2);
}

.btn.ghost {
    background: transparent;
    border: 1px solid var(--glass-border);
}

.btn.small {
    padding: 6px 8px;
    font-size: 13px;
}

/* result area */
.result {
    margin-top: 12px;
    padding: 12px;
    border-radius: 10px;
    background: rgba(255, 255, 255, 0.03);
    border: 1px solid var(--glass-border);
    font-weight: 700;
    min-height: 42px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.result.small {
    min-height: 36px;
    font-size: 0.95rem;
}

/* explain */
.explain {
    margin-top: 12px;
    padding: 12px;
    border-radius: 8px;
    background: linear-gradient(180deg, rgba(255, 255, 255, 0.02), transparent);
    color: var(--muted);
    font-size: 13px;
}

/* learn small */
.learn {
    margin-top: 12px;
    color: var(--muted);
    font-size: 13px;
}

/* footer */
.footer {
    padding: 12px;
    text-align: center;
    color: var(--muted);
    font-size: 13px;
    border-top: 1px solid var(--glass-border);
    margin-top: 20px;
}

/* focus outlines */
input:focus,
select:focus,
button:focus {
    outline: 3px solid rgba(255, 111, 97, 0.25);
    outline-offset: 3px;
}

/* responsive */
@media (max-width:980px) {
    .container {
        grid-template-columns: 1fr;
        padding: 0 14px;
        gap: 16px;
    }

    .row.double {
        grid-template-columns: 1fr 140px 140px;
    }

    .panel {
        padding: 16px;
    }

    .brand {
        font-size: 15px;
    }
}

@media (max-width:420px) {
    .row.double {
        grid-template-columns: 1fr;
        gap: 8px;
    }

    .inline-row {
        flex-direction: column;
        align-items: stretch;
    }

    .controls {
        flex-direction: column;
        align-items: stretch;
    }
}


/* Dropdown readability fix */
select {
    background-color: var(--select-bg) !important;
    color: var(--select-text) !important;
    font-weight: 500;
    padding: 10px 14px;
}

/* Result box spacing fix */
.result.small {
    min-height: 42px;
    font-size: 1rem;
    padding: 10px 14px;
}

/* Button hover feedback */
.btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(255, 111, 97, 0.2);
}

/* Formula section upgrade */
.learn {
    margin-top: 14px;
    padding: 12px;
    border-radius: 10px;
    background: linear-gradient(180deg, rgba(255, 255, 255, 0.03), transparent);
    color: var(--muted);
    font-size: 14px;
}

/* Accessibility outline contrast */
input:focus,
select:focus,
button:focus {
    outline: 3px solid rgba(255, 111, 97, 0.35);
    outline-offset: 3px;
}

/* Mobile spacing upgrade */
@media (max-width:420px) {
    .inline-row {
        flex-direction: column;
        gap: 12px;
    }

    .controls {
        flex-direction: column;
        gap: 12px;
    }
}