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var(--border);border-radius:var(--radius);padding:20px}.subtitle{color:var(--muted);margin-top:0}.calculator__form{display:grid;gap:12px;max-width:360px}label{display:grid;gap:4px;font-size:14px;color:var(--muted)}input,select{padding:8px 10px;border:1px solid var(--border);border-radius:8px;font:inherit;color:var(--ink);background:var(--surface)}button[type=submit],.problem__feedback button{justify-self:start;background:var(--accent);color:#fff;border:none;padding:9px 16px;border-radius:8px;cursor:pointer}.calculator__result,.problem__feedback{margin-top:16px}.calculator__error{color:var(--err)}.solution-steps{color:var(--ink);line-height:1.7;padding-left:20px}.is-correct{color:var(--ok);font-weight:600}.is-incorrect{color:var(--err);font-weight:600}.layout{min-height:100vh;display:flex;flex-direction:column}.layout__header{position:sticky;top:0;z-index:10;display:flex;align-items:center;gap:20px;padding:12px 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